Besides Steve's reasons, it would also depend upon WHY you decided to cancel the agreement. A deposit is a commitment and holds both buyer and seller.
If the reason is if you suddenly can't afford it, too bad. Your fault. You shouldn't have made the agreement unless you were prepared to go through with it.
If the reason is the merchandise is not as advertised, then you have a case. Not your fault. Your due diligence discovered the seller misrepresented the item. Contracts are generally non-binding if they are based upon a fraud.
Good luck.