>>58867 (OP)
I don't know where you live, but at least in most of the US you can do an Internet search for "pre-purchase inspection services." You will need to make an appointment with the dealership and with the mechanic and it may cost several hundred dollarydoos, but it reduces the odds that your new-to-you "pre-owned vehicle" will burst into flames on the way home.
When the salesman says "we don't know anything about these cars! no inspection has been done! but we think this one's in pretty good shape!" that is a warning. They buy and sell these vehicles and there is very little they don't know about anything on the lot. "As is," "mechanic special," those almost always mean it's got a lot wrong with it that's not worth fixing.
But, yeah. Pre-purchase inspection. Or maybe you know a mechanic who'll do you a favor. Without someone to look over the vehicle you're rolling the dice and taking the word of people who are in the business of marking up and flipping rusted-out deathtraps they purchase at police seized property auctions out of state.
Of course, even the pre-purchase inspection can't tell you everything. The dealership isn't going to let the mechanic disassemble the transmission to examine it, and if they'd permit it, the labor charges would probably exceed the cost of the vehicle. But without someone to do an inspection, you may spend thousands of dollars and end up with an expensive lawn ornament.
https://youtu.be/kzim1iYhmGA?list=RDkzim1iYhmGA
Good luck.