1 rule I have learnt when selling anything. Money written on anything that is not cash is not cash. ALL cheques, money orders etc etc take time to clear, Paypal is not even safe, i.e. if you allow the buyer to take possesion because you get a receipt from paypal, they can cancel the payment and you lose both item and money.

DO NOT allow possesion until the cash is in your hand or it has definitely cleared into your a/cc and is AVAILABLE FOR WITHDRAWAL.