Christ, what an idiot. The "your decision to take..." sign-off is deliciously stupid.
The good news for you is that if this is the quality of response from the owner's son or nephew or whatever, you're probably dealing with amateurs who will be scared off pretty darn quick by a letter from a lawyer with a downtown address. Unless they're stupid enough to believe their own garbage- they took your deposit, so how could it be a "quote sheet"? Even if they have convinced themselves, a letter should do it.