Those folks have been reading some of those late night info-mercial books on how to get rich in real estate. How to buy with no money down, and get cash at closing.
Fire your agent and let her broker know. Bust the other broker with whatever Washington has as a Dept of R.E. and let the lawyers have at it. If the contract specified a deposit, you ought to be entitled to it.
At least you know your house is worth $312,000 not $295,000, another smack for the agent who underpriced it and left that much $$$$ on the table.
It could have been worse, at least you are only out a few bucks and some time.....and not a ton of $$$$$$ too.