I sell because I want to try different pieces, its part of the hobby I enjoy and I don't want to have 20 amps and preamps laying around. It is rarely (ever?)a case related to the sound quality of the piece, most every piece I've had sounded good to my ears, though they often sound different and ultimately a matter of system matchups and personal taste. In the past year or so I have sold a CAT SL1, and Lamm LL2, Placette Active, Music Reference RM9 and 10, and a Pass XA30.5 - each was an excellent sounding piece, but without Audiogon I would never have been able to enjoy each in my system for time they were here.
I would only care if you were selling an item that was broke and you lied about it, otherwise it is your business why you are selling and I'll decide if the price is fair to give me an opportunity to try the piece.