Kelly. I did something like this for years. I always got a contract
from the "seller" that spelled out my commission or finder's fee, or
my cost . Don Alm has more detailed info that might be helpful.

There are plenty of other details, but this contract is paramount.
Both the "buyer" and the "seller" are going to be tempted to by-
pass you.

In fact don't be surprised if either of the parties asks you to take
less than your contract stipulates if the deal gets up in a few
millions.
Capt Charley