I had a bad experience with paypal where someone bought a key off me.
Then 30 minutes later they declared that their card had been used fraudulently.
Paypal refunded them and they got to keep the key and give my software away for free.
When I googled the postcode for the member I discovered that their registered address was in the middle of a docklands area in Inverness Scotland.
So my suggestion is that if you use paypal you verify the credentials of the buyer before sending a key - I would not want you to learn the hard way as I did...
Continuous effort - not strength or intelligence - is the key to unlocking our potential.(Winston Churchill)