I've bought a couple used small digital point-and-shoot cameras from Amazon sellers. Not a problem at all. I will say, I did choose 3rd party sellers with a good rep, and who provided pictures of the actual camera for sale.
There's also
Amazon warehouse deals, you can sometimes find a good one in there.
Payment is the same as buying anything through Amazon. Pick one, put it in your cart, and check out.
All Amazon sellers are required to accept returns, so no worries there.