Shanghai Changshuo rebate is the intermediary to write a contract?

Best to write a contract. In general, the intermediary commitment to return the fee is necessary to return, if there is no contract, then you have to sign a letter of commitment, if the letter of commitment is also not signed, then the two sides agreed to something oral, so customers must keep a hand, leave yourself a proof, it can be a recording of the phone call, it can be a WeChat chat records.