No used car lot/site is 100% reliable. Everyone, no matter who they are, has something to hide concerning their used car. Whether it's something as small as a broken stereo, or as bad as a rebuilt title. People will hide the smallest things in order to stop you from haggling down their prices. When you're looking at the car you want to buy, YOU CAN NEVER SPEND ENOUGH TIME looking for flaws. Never. If the salesman gets impatient, obviously there's something he doesn't want you to find. Never take generalized wear-and-tear assessments at face value, always give it a look-over yourself.
Check air conditioner and heater. If they're broken, it's often signs of impending mechanical failure.
Make sure the miles they advertise are "original miles". Sometimes people will drop newer engines in an old car, which resets the mileage, but that doesn't mean the transmission or anything else in the car is in the same condition as the engine.
Check all latches, hinges etc. It's a small worry, but trust me. You'll absolutely lose your shit a few months into car ownership if it turns out the cupholder is broken, or the glovebox doesn't open etc. My last car had a broken cup holder, and I didn't learn so until I pulled out the holder, put my drink in it, and watched the entire thing fall out of the center console under it's own weight and spill everywhere.
Check the radio/cd player to make sure it works right. That shit can cost a lot to replace or repair.
Check tire tread.
Check for cigarette burns. The car might smell nice now, but if it was owned by a smoker, the deodorizers they soaked the car in will wear off eventually and you'll be stuck with a nasty ass smelling car.
