basically, a legal agreement, is any document that's prepared for two or more parties, that by signing, agree to adhere to, the stipulations contained within, that guide the transaction/obligatory process to completion or for an interval expressed.
here is link to sedo's brokerage application and process
https://sedo.com/member/brokerage/index_buyer.php?tracked=&partnerid=&language=us
see TOS link in bottom paragraph
suggest reading carefully, then compare to others and draft your own accordingly
Good Luck!
imo....