The only real red flag is a seller that won’t let you take it to your mechanic for a pre-purchase inspection. “What ya hiding guy?” A lot of us like to think we’re a good judge of horse-flesh, so to speak, but if you can’t walk under it and shake the wheels, bang on the underbody with your fist, check for history codes, and examine the under-vehicle seams, while comparing your findings to 20 years of experience with said type of vehicle, you might as well be taking it on faith. Personally, there ain’t no room for faith in my business dealings. Sure, a pre-purchase costs a little money, but maybe for a little, you get to avoid a lot. Post-purchase inspections are way more expensive, because you’re already stuck. I don’t like being stuck.