M.
I can't imagine why a realtor would say that you don't owe them for selling your house for you...that they'll just collect on the new house once you purchase, unless they are a friend and know that would mean only the seller of the new home would be paying them. However, My guess is that he/she did this because you are "upgrading" to a bigger/more expensive home/area and he/she knew that if they sold your house and you used them for the new one, that you would be loyal to them and they'd make much more commission on the new house?? Either way, you owe them for selling the other one.