trying to clarify assignments

[William MacBride]

In an assign deal does whoever's assigning the contract to the end buyer always get the contract first and include the "or assigns" verbage when he signs?
I seem to be reading in some places where the middle man doesn't even sign that first contract - it's between the seller and the end buyer, and the investor (or whatever you want to call the middle man), gets put down as a "line item" and gets an "assignment fee." How does the middle man get an assignment fee if he didn't put the house under contract himself? I realize this is just a simplification of the paperwork but why is it called an assigment fee if, technically, a contract was assigned from the midle man/investor to the end buyer.
Can anyone clarify any of this - whether it's legal, what kind of negotiations have to happen between the seller and the middle man/investor, and what forms you would need?
Actually if anyone could tell me what forms you'd need in the first case also I'd appreciate it a lot.

note: this is the paragraph I read in wikipedia in their article about double closing:
"To simplify the transaction, the middleman may make one settlement statement directly between the purchaser and seller and take his profit as a line item on the settlement statement. This line item is usually on the purchaser's side of the statement as an assignment fee. This may create a problem for the middleman, as assignment fees may be taxed at a different rate than short-term capital gains."


thanks,
Will