What kind of commission is due?

[Stone Teran]

A real estate agent I know was the listing agent for a building sold a year ago.  I was neither the buyer nor seller.  He called me for a different matter and I asked him for contact info of the current owner of that building.  He called the current owner and came back with a confidentiality and non-circumvention agreement for me to sign.  He's going to take a cut of this transaction which I guess will be priced into the sales price.  Did I make a stupid move by essentially adding a middleman?  Is it customary for him to take a lesser than normal commission since he hasn't done anything?