The million dollar question, and the answer is ---- You Don't. You don't know if the other person will buy you the money or not, that's why it's illegal in PRO to "buy coins", you can just buy coin related items, like MS, mount, etc. If you look at the paypal url when you buy coin, your user name and server is inside the query string, and that's how PRO knows who to deliver the coins to and which server. You can change the query string to someone else's name and another server, and the coin will be delivered to that person in that server. However, you don't know if the seller is going to actually buy you the coin; if you pays first, and he doesn't buy you the coin, you are pretty much screwed.