I just clicked "buy it now" for a camera on ebay. Now I might want to get it elsewhere. What happens, can I cancel it, or am I bound? Will I get negative feedback etc?
You can't cancel it, but the seller can. If you ask nicely he might. If he doesn't, then you can simply not pay, but he will start a non paying bidder dispute with you. Get more than 3 of these (at least I think it's 3) and eBay will suspend your account.
Sellers can't leave negative feedback for buyers anymore.