The title says it all...
What are your stories that make you cringe when you were selling (or buying) an instrument?
For me it happened last year. I needed money so I had to sell my much beloved Fender P. It was nothing luxurious but I loved it... MIM but sounded fantastic. Had many a compliment on my tone.
Anyway... I had a few interested people but most were no shows but this one guy comes in to try it out. No problem there... he plugs in to my amp and sets the EQ flat... again, no problem. He plays a few notes, then stops... looks it over, down the neck, etc... checking that everything is in order. Still no problem, the bass is in excellent condition. He then puts his right hand at the base of the neck and his left at the headstock. He pushes in towards himself with his right hand and out with his left. I hear a fairly loud crack! I'm thinking.... *** is he doing!?!?

I swear I almost punched him in the head! He then looks at the neck joint and says "there some cracking in the finish there." No kidding!!! You did that! All I say is "So you have the money?". He says, "Yeah, sure. I'll take it." You bet you're taking it! I take the money and quickly escort him out. As much as I loved that bass... I hope he actually damaged it! Bastard!
Your go!