I think that is not a clear scam. But it is a form of fraud
I guess that OP needs the Facebook account for advertisement. He will initiate facebook campaign with your FB account, and will not pay for it because Facebook does not insist for payments before beginning advertise campaign. After months days, FB will ask you to pay for this campaign. You can still to use your account, but you will have obligations for this money.
He will get payments from our client for advertisement, for example, $50 and he will pay you yours $10-25. but you will be unable to use your FB account for advertisement until you pay off this $50
This is a complete scam stay clear