If you’re looking at trucks then it’s okay to pay a mechanic to do an inspection if you’re too traumatized to do that yourself and can’t spend willpower, like just look at the truck and get a sense for it, and if you’re too traumatized to think then err on the cheap side and get something with a decent interior that runs enough to be moved, and use your brain on your second vehicle.
If you have a bit of energy I’d recommend getting a diesel (make sure it does diesel) scan tool, I used this one, and check what codes come up (and if the smog indicator is green/yellow/red). Google them so you know what they actually mean and how big of an issue they are. If you’re keeping a vehicle for the long term e.g. actually maintaining it rather than doing the bare minimum to make it run, engine problems are the most expensive thing that can go wrong, so in some sense the point of the scan tool is to see if anything is wrong with the engine internally. Get a flashlight/phone and look for oil leaks and other fluid leaks, both ones you can see from above the engine bay and ones from crawling under the car. If you see a leak (most cars in your price range will have one), see where it’s coming from, e.g. look up and find the highest point that that leak is coming from, probably at a gasket/crease between two parts of the engine. Things in the middle rather than top of the engine are harder/more expensive to fix because you have to take off more components to access them.
Most car work is just, take out five components to be able to reach/unscrew something that’s broken, then buy a replacement of that part for your make and model off of RockAuto (cheap)/O’Reiley’s (same day and you can ask for advice) and put it where the old one was. O’Reiley’s is weirdly good about always having one person with mechanical experience on staff at all times and most other auto shops aren’t, so try asking them for advice if you’re stuck halfway through a repair. Like they’ll tell you to spray rust penetrant and use more leverage/a longer breaker bar and buy a torch to heat up a bolt if it’s stuck and you’re trying to get it off, in that order, and can fill you in on unknown unknowns you might not have thought to ask if you’re stuck. Also you can rent specialized tools to do specific things like removing a stuck oil filter, for a refundable deposit.
At some level engine inspection is trying to determine if the previous owners have changed the oil or not, since a lot of how well the engine will work is downstream of if they changed the oil. If the oil was changed in the last 500 miles (check for a sticker on the windshield or just check the oil and see that it’s too perfectly yellow) that likely means they only changed it recently because they wanted to sell the car, or if it has been more than 3000 miles (if normal) or 10000 miles (if synthetic) since the oil was changed then that vehicle has been abused. The oil will be black if it hasn’t been changed for a while. Oh and check the oil level itself, if it’s low that means it’s been leaking.
The four primary fluids that might be leaking would be engine oil (yellow to black), coolant (tealish, smells sweet), power steering fluid (red), brake fluid (opening the brake fluid container makes the fluid go bad much faster), in that order of probability. Determining what fluid type a leak is can help you trace it back to the source faster. If you don’t know if something that looks dirty and just barely damp is an engine oil leak or just dirt, swab it with a paper towel and see if the towel gets wet or just dirty. Though if it’s that unclear you aren’t losing enough fluid to matter. Unless it’s dripping onto a hose, which will cut the lifetime of the hose in half. There’s also transmission fluid and rear differential fluid (shouldn’t be leaking, and I expect nearly every car to be overdue for a rear diff fluid change, though you can put that off without much repercussion if you have other priorities), and oil internal to the ac compressor pump. The AC compressor pump is almost always leaking a tiny amount of oil, and if you want to make your AC compressor pump last longer it’s good to run the AC (not just fan) for a couple minutes once every few weeks so it gets lubricated; this isn’t integral but older vehicles that have sat without driving typically have bad AC and the root cause is that the compressor hasn’t been run regularly.
[All the diesels I’ve looked at have this tube on the very bottom of the engine that’s dirty and has oil dripping from it, what is this?]
On a diesel, check if the oil is milky or white, and check if the coolant is milky/has oil in it. If your coolant and oil is mixing then you shouldn’t buy the truck (unless it costs like 1k). You can check blow-by. If the exhaust blows colored smoke that’s bad.
If you can check the transmission fluid, see if it’s rusty, if so that means the transmission fluid hasn’t been changed regularly and you will not want to change it, because if it has never been changed then changing it may break the transmission. If it is clean/not rusty/has been changed then you should actually change it when you’ve bootstrapped to the relevant level of willpower to be addressing things at that level of urgency (I expect once you’ve gotten your long-term actually-going-to-maintain-it slackmobile past minimum viable product status). Transmissions with changed fluid > transmissions with rusty fluid that work normally when driving > transmissions that kick/slip. Transmission issues are the second most expensive thing to fix on a vehicle. Electrical issues are the third most expensive but I’ve never fixed one; electrical issues will show up on a scan tool. If you replace a component and the relevant error doesn’t stop showing up on a scan tool you can clear the codes and/or start the engine/drive it around four or five times including highway driving to see if the code clears on its own (some codes won’t clear until you e.g. do five miles of highway driving without a sensor firing at all), and if it doesn’t clear after that then it’s an electrical/sensor issue.
Take the car for a test drive, notice anything weird (does the car brake well and speed up well if you slam the gas/brakes, does the engine stutter when running or starting, does it idle cleanly and sound like a normal car engine overall, etc), check if the lights/signals work, and check if there is any play in the steering rack. Play as in, if you are steering right and then turn the wheel left, how much do you have to turn the steering wheel before the car starts turning, e.g. how much dead space where turning the wheel doesn’t do anything is there? Steering racks aren’t important to fix unless you want to maintain the car well, but they are expensive, because you have to put the car on a lift e.g. you can’t do it yourself.
Try to make your turns wide so you don’t hit anything, especially if you’re a zombie. You’re most likely to make a mistake when backing the truck, I recommend actually getting out of the truck and looking at what’s behind you before parking. You can view and test drive a truck you don’t expect to like if you’re a zombie or you want to build your driving confidence a bit before looking at one for real, which can let you look at engine components and realize you don’t know what they are and then google what they are.
The steering system will be quite a bit different depending on whether it’s an ex-uhaul ford or a mitsubishi fuso/Isuzu/International, the latter don’t have all the same suspension components that the former do. Either way, look at the wheel from under the tire, see if any of the rubber parts on things attached to the wheel (lower control arms, and outer tie rods plus upper control arms if applicable) are cracked or dry or are not supple to the touch. If so, then your car won’t hold an alignment and the tires will wear faster, and also you won’t pass inspection if the inspector is strict/by the book. FWIW you can grease most of these components with a grease gun by unwrenching a bearing on the top of the components and fitting the tube from the gun on it if you really want them to last longer, and if the components on the car have been greased and nothing major is wrong, then the vehicle has been taken very well care of for as long as the current owner has had it. I really wouldn’t expect to see greased bearings though.
Ask why the seller is selling it. I’d never buy anything from a dealership or reseller/person who buys cars and fixes minor things then resells for profit. Buying from individuals or small businesses is good. “I bought it because renting the same truck from Uhaul would cost 2.5k and I planned to sell it” or “I ran a party supply store and we’re going out of business” are good reasons, the encompassing principle behind both is that someone who was actually using the truck is selling it. About half of Craigslist ads will not have a title, seemingly because it’s expensive to register it. This is personally a reason to write off a vehicle for me, as I want to be sure the vehicle is actually owned by the person selling it, but YMMV.
If you’re buying a vehicle in California check the CARB regulations, they only apply to diesel vehicles with GVW of 14,000 or higher. (GVW is listed in the cab or on the side of the door, you can check it with the VIN (if you’re paranoid you can see if the VIN from the vehicle matches the VIN from the scan tool matches the VIN from the title)). Basically if you have a diesel vehicle with model year 2010 or older, and GVW is over 14,000, you can’t register it within the state of California commercially, but you can register it as an RV. This means that those vehicles are cheaper than similar gas vehicles, since there’s limited demand. OTOH the main trucks that are gas powered are Ford ex-uhauls (they look pretty characteristic, all have a grandmother’s attic that extends above the cab), and they use a lot of the same parts as normal Ford cars, so they may be easier to find parts for in collapse scenarios. Everything about them is basically engineered to be idiot-proof and come with pre-drilled studs/railings you can screw stuff into, because Uhaul’s business model is leasing big trucks to zombies with no mechanical or truck driving experience. The main downsides about them are that their engine bay is tiny so you’re going to have to take out way too many components if you’re fixing anything in the engine bay. Probably because the engineers designing it wanted to make it short so zombies didn’t crash it. The sort of truck where you pull the cab up onto a stand to access the engine is more “scary” if you’re going into this while suicidal, but I expect it to be better for a long-term vehicle. Also I’ve never worked on a diesel vehicle, but diesel engines can last much longer. I expect a diesel truck to be the way to go in general.
Check the hoses in the engine bay by squishing them and seeing if they are supple, they’ll need to be changed soonish if not. Hoses are easy/cheap to repair but bad hoses are a barometer of the vehicle being poorly maintained. If the engine belt has tiny cracks in it it’ll need to be replaced, if any of the components on the engine belt are leaking then you can ignore them for a while but might want to replace them if you’re actually maintaining the vehicle.
Some rust on the vehicle is fine but if the bottom is covered with rust that’s bad. Go through a car wash that sprays water up onto the bottom if you drive on a road that’s been salted and you’re not going to drive on another salted road for a couple months.
I expect there are diesel-specifc things I don’t know to check. IMO it’s fine if the key needs to be in and partially turned for 10 s before cranking the engine so the glow plugs can warm up.
Having a door other than the rollup rear door is nice if you’re going into this as a zombie, so you can get to a minimum viable product with less work. If you’re entering the vehicle from the rollup door, you can typically put the lock in the same position it would be in while locking the vehicle from the outside and this will prevent anyone from locking you in while you’re inside, e.g. do that before entering. I expect you could then use a hook and eye door latch to then lock the vehicle from the inside as a temporary solution (maybe?, would the walls/door be thick enough?)
That’s as thorough an inspection as a mechanic would do if you paid $150 for one, and now you can mention the things you noticed wrong with the vehicle when trying to bargain for a lower price.