Broker is requiring CSA (I am the buyer)

Hey guys. I would love some guidance on this, as this is the first time I have encountered this situation.

A seller's broker (I have purchased a 16 unit apartment from this broker before) is trying to get me to sign a CSA that has me paying out 5-6% of the sale price. I am the buyer. The CSA only pertains to this property. 

I don't know much about this deal, other than it is in a market I like, and it is a 16 unit apartment complex. They won't release it to me without me signing a CA and a CSA. He says he has another buyer on it already that is interested.

Have any of you encountered this situation? Should I sign the CSA? 

Thank you, guys!