I've always bought used cars and tbh I've done the standard checks that most will do, walk around, test drive, check for scratches etc.
Nearly a year ago I bought a 1 year old approved used BMW form a main dealer, looked perfect etc. Only to find out that it was in a huge crash with subsequent repairs to go. Overspray, respray lines, weld repairs, even bloddy masking tape! List goes on. The car has long since been returned, see my post about it as it will help with where/what to look out for.
https://g20.bimmerpost.com/forums/sh....php?t=1706667
So since then I have picked up some skills in for more in depth checks such as, checking the paint colour matches, any over spray in hard to reach places (door joints etc), running my finger on the door lip to see if theres a respray line, checking under the car to see if there's any clips or bolts missing, even checking if all the weld joint look original.
To some this might be overkill but with the crap I went through with that car I'm not making that mistake again. I even did those checks on my replacement (pre reg 1 year old) as I've heard dealers have a margin of 15% damage on arrival (not sure about the %) which they fix, most likely without telling you.
In short, it always pays to do some in depth checks.