Oh..the anger!!!

So we got an offer on our house, awesome. It was quite a but lower than our asking price, but we negotiated and brought it up a bit. Then they asked for a little extra money to put in another A/C unit. Okay. The contract was written up, signed, the paid their earnest money. Then they have 10 days to back out for any reason. We waited it out and they said they were very committed and we would close at the end of the month. Then we get an email this morning saying that they have thought it over and they want out. Apparently the lady has hip problems and is worried about getting up and down the stairs. Hmmm.... isn't that what the option period is for? to change your mind? I am just livid? I mean what is the point of a contract if it isn't binding in any way? They are even getting their earnest money back! How ridiculous! I seriously want to punch someone in the face.