If the seller has decent feedback and the pictures look good. Read through the description thoroughly and if it seems like something you still want, buy it.
Ebay protects it's buyers pretty well. If anything is not as described immediately contact the seller, if you end up not happy with their solution then you can contact ebay. I've had great experiences on ebay but just remember that if something is too good to be true it might be.
Look out for low feedback sellers, sellers that have not sold anything in years and all of a sudden are selling things unbelievably cheap. Just use common sense and you should be fine. Even then eBay should have your back but it's not worth the hassle.