My car came out clean on carfax. However, after someone pulled out in front of me, the shady repair shop swore that it'd been hit before, invoking the "prior damages" clause of my insurance.
I thought they were full of shit until I pulled up the carpet and found glass, lots of it. I put that together with the passenger seatbelt that goes the wrong way, and the newer looking plastics on the passenger side, and I'm pretty sure it'd been hit before.
It's not that big of a deal, considering I paid less than 60% of Blue Book Value.