That's easy to answer; he'll use stolen credit cards to send money to your PayPal account, you send him 90% of the money, and "keep" 10% for yourself (lol,) then when the people who's credit cards/identity was stolen find out, they charge back from your account.  The OP is long gone with short con.

Another thing worth mentioning, this thread shouldn't be in this section.   Maybe it should get moved straight to scam accusations.