Did your broker work hard to get your home rented? Do you think that since he or she worked hard to do this that they deserve a commission if the people there decide to buy the property? After all, it was the broker (and his advertising or contacts) that bought you guys together to begin with. Correct? Also, keep in mind that the commission you paid your broker for the rental, probably wasn't sufficient to pay for your broker's gas money. All of this is the real world. The only way your broker really gets paid is if you pay him/her a commission on any future sale. So, ask yourself, do you have to pay him/her? Legally, if your broker didn't include that provision in thelease, than you are not responsible. But, morally, you have to live with yourself.