There is no law regulating the code of conduct in relation to "rent commission". When, an agent or a broker is asked to find out a property on rental, the broker would render the services and for which he would be expecting the "service charges, or what is popularly known as commission". The payment of commission, or a remuneration for services rendered would depend upon the terms and conditions. These are all matters, where no written contract is entered into. It is all executed in good faith. However, in your case, there appears no express term for making of payment by tenant. But the mercantile term, condtion, custom and usage is to pay the commission. And again, if you verify, the broker is such a community that it would charge the commission from both the side. So, if it is not a bigger amount, pay it , and hereafter, be careful to enter into clear terms to avoid bitterness.