Boy I've been burned so much with electronics and power tools that I abide by what diggumup said - always test on site, and even if it works always assume the battery will need to be replaced.
I once sold 24 Eisenhowers on craigslist for $65 (if they took the whole lot, I was charging $3 apiece otherwise). The kid had a scale, and had his iPhone open to a coin website. I gave him fifteen minutes with his gadgets and he must've decided they were silver and he was pulling one over on me. he bought 'em all. If he had asked me if they were silver I'da told him no. But I'm not going to sabotage a sale by pointing out the obvious to him. especially considering he thought he was pulling one over on me. Never did I say or hint they were silver. I was marking them up because the military around here uses them for graduation in the spring, and they have a tough time finding them, opening up the market.
Anyways I get an email the next day from him that says I really made out on him on that deal. I was wondering, what does he want from me, for me to say "ok you got me, I'll give you a refund?" I never would have given him a return in a million years. He was trying to make money off me and I ended up making money off him.
Point of this long story is that these are how these deals go. you have the time ON SITE to determine the value and make an offer. As soon as you part ways, deal is done. However, I would also say the exception is if the person was intentionally deceived. In that case, all is fair game
