I had a beautiful custom painted TC body about 5 years ago. Bought it trackside, painted but not cutout as ''it was a custom order, but the guy backed out of it''. It was offered to me for £30 which is fairly cheap for a custom painted TC body.
Cut it, mounted it and ran it for the finals that day....and prompty saw 75% of the paintwork flake off. It turned out the ''custom painter'' had decided to experiement with acrylic paint and it didn't stick.
Also I've purchased various chassis with hidden horrors like ball diffs with just 3 or 4 balls in, a TC where every screw was threadlocked in and rounded off when tried to be unscrewed, and a Tamiya Mini that didn't have any bearings OR bushings in it!
Oh, and a classic one for me at Worksop in 2001/02 when they ran TC. I bought a Schumacher Axis 2 complete with body and wheels/tyres secondhand trackside. My Yokomo YR4 was a bit old and tired, and I was too tempted to run the Axis 2, so after the first round of qually I'd swapped over the electrics and made sure the tyres were legal. After putting the car down and going round the first corner, I should have checked the tyres were actually glued on....