You can't win any dispute with Paypal they also on the site of the buyer, which is good if you are the buyer but as a merchant it is very bad. In regards to this PayPal sucks really big times.
It should at least be possible if you are able to provide prober documentation that they will look into your business case but they don't. You just get a stanard reply from them, we decided in the favour of the buyer!
I had never heard anyone winning a dispute against PayPal and they can't win too. In their user agreement PayPal states that any disputes would be only handled at the courts in their locality which many people won't approach on most cases.