I've never encountered problems with ebay yet (fingers crossed). I experienced 3 items that didn't arrived from 3 different sellers. 1 gave me a full refund, 2 resent the items which eventually I received in the mail.
A note to anyone who intends to use ebay/paypal, if you didn't receive items, you can open a dispute case.
If the seller sold you a fake watch and insists it's genuine, Paypal can't help you and will ask you to settle it with the seller.
If the seller sent you an empty box, you're screwed which is the case with a Seiko member on WUS forum.
On sales forums, it's not just the buyer who has to be vary of the seller but if you flip watches, you should also be vary of the buyer. A buyer can scam you as well. I receive emails from strangers who are "extremely eager" to buy my watches and I often prefer not to deal with these kind of people. They are often from certain countries which I won't mention here.
One other thing you could do to verify a seller/buyer on sales forums, is to ask to be added as a friend to his facebook account. Once added, you could see whether he's a real person or not, with real activities, updates, etc. You could also do a search on his email, genuine parties would show some results. I believe many of us here or in other forums would have a facebook account.