I was an avid eBay-er for quite a while. Besides the occasional "useful" purchase, it's quite helpful for collections (I like movie posters and unique Converse All Star sneakers).
For most of the time, I used PayPal, which is the ubiquitous form of payment on eBay these days. Basically, PayPal is a service that allows you to pay (and receive) moneys through either a bank account or a credit card. It works rather seemlessly, and almost all volume-sellers on eBay prefer, if not require it.
One day I got an AmEx bill for $2,500 from PayPal. Someone had managed to crack either my eBay or PayPal account and do a little scamming. Well, AmEx took care of it right away. When in doubt, American Express rocks your socks. They're amazing and come as highly regarded as any financial institution could be.
Unfortunately, the same can not be said for PayPal. They have a little-known policy of freezing accounts and inactivating them if there are disputed charges and not dealt with through PayPal and PayPal alone. In other words, if someone manages to scam you and charge your credit card or bank account through PayPal, PayPal itself wants to deal with it and not even alert your bank or credit card company. They recently settled a serious lawsuit over this and I, along with a few other million folks will get a couple of bucks back.
In short, all of my experiences with eBay have been fine, but PayPal is an unnecessary evil that should be avoided.
N.