I know this problem. It is one of my oldest problems with paypal. Here are some other problems regarding paypal : paypalsucks.com
If you are offering consulting services, you have no way to prove that you've offered this to the client. So, if he is a scammer...he can ask a refund. He will definetly get his money back. Unfortunately...that's the truth.
Fight for it. If you are right at every stage. Keep updating the conversation's. but it also depend on the payment amount. for example, if the amount if 5 to 15 dollor then its a waste of time in arguing as your account will be on hold for that time. So you would not be able to receive any payment on the a/c. [I think so. if you can receive but you can't widthdraw in any case.] If payment is more: then i would sugget I have posted the item and I can provide proof that the item was posted through an approved postal service to the address on the Transaction Details page. Show all the email's to paypal. This will work! All the best!
They will not help you if you just email them, try to call them if you need a good support From PP. Good luck