The ancient Romans had it right: Caveat emptor.
A friend and wise old owl sometimes debates with me over buying used. "There's a reason why they're selling it," he says, "and you're going to find out what that is."
In my experience, usually it’s not something catastrophic (that becomes pretty apparent when you see the thing), it’s something that’s a half hour fix and the person selling it was just ignorant of it. I’ve lost count of the amount of “broken” stuff I’ve bought for half price thinking I was in for a project, when all I’ve had to do was just replace a cheap part.
The idea that we live in a society of “disposable” goods is more belief or lack of understanding than it actually is the case. I'm sure many have thought they were pulling the wool over my eyes, but they were actually shooting themselves in the foot because they didn't know any better.