Now therefore, please swear to me by Yahweh, since I have dealt kindly with you, that you also will deal kindly with my father's house, and give me a true token;
The two spies did attach one condition to their promise, that being, that under no circumstance would the woman betray their mission  (Joshua 2:14).  Also, there was the agreement that the identity of Rahab's house would be indicated by the red cord.