Contract with Seller's Lawyer??? OR How to protect myself?

[Ingrid Bailey]

Lawyer contacted my company - has a client who wants to sell GROUPS of his properties in three different areas.  I have a buyer and we're ready to put the play in action, but I need to know what I should put in place with seller's lawyer as the designated person to sell the properties??  In other words, how do I protect myself (from buyer cutting us out of deal)?