I occasionally browse eBay and Junksale.co.uk for ham radio equipment. It simply amazes me the number of times I read in the item description something like: "Not tested but believed working, no returns" or "Last used several years ago, was working then, no returns." Do sellers really expect buyers paying a large sum of money for an item of used equipment to take a gamble that it is working?
If I was selling something I hadn't used for a long time, or something I had never used (for example, something I was selling on behalf of a SK) then I would test it before selling it. I would certainly then be reluctant to allow the buyer to return the item having ensured that it was working when I sent it.
If I really was unable to test the piece of equipment then I would allow the buyer to return it if found not to be working, and state that in the advert. Otherwise I would state "sold as non working" and expect the price offered to reflect that. But to state that you aren't sure it is working and then also state "no returns accepted" sends only one message to me - that the buyer knows or suspects it doesn't work and wants to find a mug to off-load it.
Do people actually buy things under these conditions?