Let's look at it another way - picture this scenario:
You're selling a vac on eBay. It's in very nice condition, but it isn't a very rare or unusual model. You expect to get about $50 for it, if the right bidders see it. You check your computer after the auction ends, and nearly fall out of your chair when you see it's sold for $750.
Would you really contact the winning bidder and say, 'I can't, in good conscience, accept $750 for this machine, it's just not worth it; let me refund the $700, and you can have it for $50.'
???