Final answer:
The best description for this type of agreement is an implied agreement.
Step-by-step explanation:
The best description for the type of agreement, when the actions of a buyer and seller seem to indicate that the seller will pay a broker a commission for selling her house but no agreement has been discussed or signed, is an implied agreement. Implied agreements are formed based on the actions or conduct of the parties involved, rather than through explicit written or verbal agreements. In this case, the actions of the buyer and seller indicate that they both understand and agree that a commission will be paid to the broker for selling the house.