Flood car simple. Remove rear seat and see if got rust. If got then confirm it’s flooded. Also by opening the door and taking a sniff. If it smell musky then it’s flooded before

For accident u need to see the main joints if there’s welding mark or the pillars are intact and smooth. If any other mark then confirm it has been in accident before

Small fender bender cover up is harder to detect but the paint around the inner should be a give away

Last but not least if u feel the car has something wrong…stay away even if it’s dirt cheap vs the other cars. There is definitely a story and cheap price is used to offload the car