I have had some good and bad dealings at E bay. So if you decide to buy an E bay item from a private person here is what I recommend you do.
Under no circumstances pay cash, E bay will not give you fraud protection if you pay cash. If you have to go this way then you will loose certain amount but you will get most of your money back, so pay with MO, Check.
Print and save the add you bid and won, E bay will ask you for this if you have to ask for fraud protection.
As to the cameras, I would first ask the seller if he has a return policy, I stay away from the "as is" sales.....to me "as is"= you are stuck with the item!
Sometimes the sellers are cameras stores. If this is the case you might have to fight a little but most of the time the stores selling are reputable and you wont have a hassle with defective items.
OTOH dont get too demmanding, I bought my Korona at E bay from a guy who had no experience with this type of cameras, althought the camera outwardly looked in excellent shape, when I removed some of the metal parts it had a little bit of wood rut. I imagine someone in the past polished it with liquid polish and it got inside the metal parts. This to me was no big deal, a little bit of wood filler and patience fixed the problem. So sometimes someone will describe an item as excellent and due to ignorance it turns out not to be so, if it is in good faith, relax, talk it over with the seller and most of the time you can come to an agreement. In my case the person who sold me the Korona was a pretty nice guy and for 10 bucks I spent fixing I did not even bothered him.

IOW use good judgement, check the sellers feedback and ask for return policy.