House Hunting

So we were two weeks away from getting a house and the people just backed out of the deal. I really have no idea how they could do this since they had already excepted our offer. I guess they decided not to sell their house or wait to sell it or something. This is the second offer we have put in and this is the second time that the people have suddenly decided not to sell their house. Seriously why did you put it up for sell if you weren't going to sell it that just doesn't make sense.