I recently sold an EF 100mm f/2.8 macro lens on Craigslist for $400. I tested it at various focus distances and apertures a few days before listing it. I had no problems with it. The purchaser showed up to the transaction without a camera. Luckily, I brought one and let him use it to take some shots with the lens. I commented to him that I thought it was strange to buy a used lens without bringing a camera to test it with. He replied that he usually just looks at the front and rear elements and the condition of the lens. He took a few shots with it and deemed it worthy of purchase. He gave me full asking price with no attempt to quibble, which I also thought was odd. I e-mailed him later that day to ask how the lens was. He replied, "Its great." Today I get an e-mail from him stating that the lens is faulty, that Canon agrees with him, and that there will be a repair bill involved. His question to me is, "What are your thoughts on how to proceed?"
Does anyone have any comment on how to proceed with this? I do not knowingly sell equipment with undisclosed damage. I recently offered to sell a lens I don't use to another POTN member. After the buyer expressed interest, I thoroughly examined the lens, found a bit of fungus in it, called off the sale and donated it to a local high-school art department. I want to do the right thing, but I am afraid I may be getting gamed here.