回复：朋友办了一个经纪公司, 万事开头难, 遇到一些问题, 我自己也有

no other way, u have to make a legal contract with the related parties, specifing your rights and compensations. But it only protects this single transaction, u can not avoid being skipped in the future.
usually u have to develop a solid relationship with the seller/buyer. It takes time and nothing is free of risk.