Rule Number One:  never put money down on real estate sight unseen, unless it's through a realtor who you have learned over time that you can trust.

If the notice for the auction, or something along those lines, clearly said the property was vacant, you might be able to get your money back, because that would have been fraud.  I would hope nobody in this day and age would have been stupid enough to set themselves up for that, but if so, you need to hire a lawyer.  And if not, you're going to need the lawyer to get rid of the truck lady, and fast.  One place to find a qualified attorney is our website, http://attorneypages.com

Wow!  What a nightmare.  Only you can decide whether the amount of the deposit is such that you are comfortable walking away from - otherwise contact an attorney who handles MA Real Estate as soon as possible. 

Assuming this was a foreclosure sale, there maybe terms in the notice of the auction which entitle you to your deposit back.  You may have also signed some type of agreement at the close of the auction which could help you.