Document to keep from getting back doored on a deal?

[Darvin Ezell]

Recently I have been making alot of connections with some big buyers looking to purchase multi-family properties. I also have made connections with different seller reps looking to sell these type of properties. Whenever I show the potential deal with my buyers, they usually request a conference. Is there some type of agreement or document to prevent the seller from sending other deals to my buyer or doing the deal without me after having them speaking on a conference call? I dont want them exchanging contact info and me get excluded? Any help is appreciated.