if you are serious about getting into bitcoin trading, stop using paypal for your bitcoin-related payments. paypal transactions are reversible, bitcoin transactions are not. I am sure you can see the problem here...
the trick is to use TRUSTED sellers
also, NEVER accept CC paypal.... make sure there only chance of geting the $$ back is with a dispute, no chargebacks, and then you have proof so yes
you can also make them add in the NOTE that they will not chargeback or dispute the transaction as this is a sell of virtual goods and that they have received them and that they are 100% happy with them and can't change there mind as sale is final