I recently learned my lesson buying used gear. So from now on I am asking many questions about the items I may buy. Repair history, number of owners, and issues at all, etc.
I don't care shy someone is selling unless the item was not reliable or is having repair issues.
To answer your question more directly, I have purchased an item and when I plugged it on thought well not what I expected. In my mind that component would have to make a 180 degree turnaround to sound better than what I own. So in that case, back on the market it would go. It just was not better or did not work in my system.