you should be the seller if you are brokering, only communication of the sellers negotiations in pricing between yourself and the seller should take place, all communications to the buyer should only go through you, i have brokered serveral names, some big names, from big domainers, once a transaction is ready to be processed, should it go through an escrow service, have the seller initiate escrow, if paypal, i have always collected the funds, taken my 10% of the sale, and sent the 90% of the sale to the seller.