I suspect that the 3,000 is just a holding deposit (to take the property off the market, as they put it) until the remainder of the usual 10% is paid. Having said that, I've known plenty of sales lately where no deposit changes hands at all and they proceed straight to notary. This is actually what I now routinely advise because of the risk of an agent going bust while holding a deposit.
It is routinely understood that a buyer loses the entire deposit if s/he backs out of a purchase, though only last week I became aware of one agent returning the lot to such a buyer. Assuming it doesn't get returned to the buyer, however, then yes, in theory, it should go to the vendor ... but I'm not aware of that happening too often ...
M, as far as being legally bound is concerned, that legal bind is applicable from the moment in which the sale is agreed, deposit or not.