As with any transaction an element of TRUST is assumed for the system to work.

Ask the buyer to send the payment to your Paypal account. (Assuming he trusts you, he will)

THEN: either

1. Send the buyer the item (Assuming you trust him) OR wait till the payment clears. (Assuming he trusts you)

OR

2. When the payment clears (may take 5-10 working days), send the item. (Assuming he trusts you)

Bottom like is: if both parties are true to their words, it should there should not be a problem.