A buyer can file a dispute for non receipt of item OR item received but not as described.
If its the former and you can prove delivery with a tracking number then you would win. If you lost then you would have to refund the buyer and claim from the postal service if you took out insurance.
IF and only if the buyer won a dispute for item received but not as described then you 'may' have to refund him on return of the item back to you.
If its a 'chargeback' then thats not a paypal dispute, its done via a buyers credit card company (if they funded their paypal payment that way) and the card company make all the decisions. If you lost then you would be compensated by paypal IF and only IF you met all the requirements of paypal seller protection...........so you need to go and read up on it in the user agreement so you can risk assess your own transactions.
Advice is voluntary. Kudos / Solution appreciated.