As far as I know if it happens not too often the losing party just sees the money dissappear. It gets interesting when paypal can't get any money back from the person losing the dispute. I'm not sure what happens then. If a dispute is not legit the seller should be able to provide evidence that he delivered the good in guestion. Untracked shipping is thus very dangerous for sellers. There are many ways to scam, so using paypal requires trust from both sides.
When you open a PayPal claim... PayPal freezes the disputed
amount in the Seller's account and is held until the Claim is
settled.
If the seller refunds the buyer BEFORE the buyer escalates the
Dispute to a Claim... nothing else happens and the seller is sent
a Thank You note by PayPal praising the quick resolution and
refund to the buyer...
If a Claim is resolved (by PayPal) in the Sellers favor.... the buyer
is out of luck and the seller gets his funds released back to him.
If a Claim is resolved in the buyer's favor... the buyer receives
a full refund of the held disputed amount and the seller will
have a mark in his sellers file..
If too many Claims are opened against a certain Seller...
the seller could get his account suspended...