How it works is,
Step one: You have your cash with you and go to the house.
Step two: You have the owner step in side and stand in-front of the door and say !sellhouse and then the players name.
Step three: A trade will initiate, be very careful, put your money up for trade and you'll see a scroll in their trade screen and money in yours. Make sure you right click their scroll before trading just to be sure its not just a scroll, make sure it's the house agreement, you'll then after guaranteeing it's legit. Hit accept.
Step four: Click the scroll and there you have it, you have your own home!