Sounds reasonable, but this could happen: You sell a CD player in New York, ship to the buyer in California, who promptly drops it on the floor while opening the shipping carton. Said CD player won't play CD's and the display doesn't work. The next day he calls and says that the CD player quit working and he wants his money back. What do you do? The seller doesn't have the resources to investigate warranty claims, and upon examination of the CD player doesn't know why it stopped working, the freight carrier is not responsible, and I doubt that AudiogoN would want any responsibility in judging the situation. And how could they anyway? And besides, once the payment is retured and the player is sent back, it could look like it was run over by a truck or worse. What it the recourse for the seller then? Perhaps this would be a good rule: When you buy something used, assume that it is not new and not in new condition. In most cases, when you buy something on AudiogoN it is from someone that you do not know. This is not like walking into a store and buying something used. This is why feedback is used to rate buyers and sellers. If you are afraid of getting a piece that might break, then don't buy it, buy it used from a shop or from someone that you know, or buy it new.
I am not a regular seller on AudiogoN, but I am a regular buyer. I have not had a problem with bad equipment being sold here. I have a number of nice, well cared for pieces. All but a couple are well past the manufacturers warranty period. If I should decide to sell one using your idea, I would have to substantially increase the price to cover myself because I have not idea if any piece of my equipment will quit today, next month, or work forever. And I have no control over what a buyer would do with it once it was in his posession and no good way to determine if the failure was caused by misuse.
Using the policy that you suggest would surely lead to more conflict, not less.