John, a real estate broker, and Chris, a property owner, have entered into an agency relationship. Soon after, a dispute arose in regards to how much commission should be paid to John if he finds a buyer for Chris' property. What should they do to resolve their dispute

When Chris decided that John would be his real estate broker, they signed an agreement, and that agreement should have included the commission rate that John should receive.

If a dispute arises later about how much money John should receive, all they need to do is check the signed agreement and see what commission fee was agreed between them.