Ah yes, the old deposit debate. First, only a foolish or inexperienced sales manager accepts a deposit to "hold" a vehicle. The only reason anyone wants to "hold" a vehicle is so they can continue shopping in case they find something better. It makes no business sense to take a vehicle out of inventory, preventing it from being sold, on the premise that someone might come back and buy it. And although it is generally the store's right to keep the deposit if the purchase isn't completed, that is poor business practice too. Far better to decline a deposit to hold a vehicle, let the customer continue shopping, and let them come back and buy when they are ready. Unfortunately, this issue is often encouraged by idiot salespeople who don't think beyond the next hour and would love to have the whole lot on hold for their customers. I've been faced with many blank stares over the years when I've asked a salesman that wants to take a "holding" deposit, "So what if you get a customer tomorrow that wants to write a check and drive off with that car? Are you going to tell him that he can't buy it because someone else might be buying it next week?" Good thing salespeople don't have the final say over things like that.
The only time a dealer should accept a deposit is when a vehicle is sold pending the completion of payment. That is, for the time required to secure financing or to bring in a check for the balance. At that point it should be made clear that the deposit will be kept unless the deal is completed.
In this case, the timeline, according to the dealer, was deposit given on March 16 and then no contact from the customer until the end of April. In a small claims type of court case it could be easily argued that that length of time is unreasonable to expect a dealer to hold a vehicle. (There is no dealer anywhere that would normally hold a vehicle for 6 weeks for someone they can't contact.) Even if no completion date is stipulated on the contract, the unreasonable length of time and the lack of contact from the customer would pretty much sink the customer's argument. Just because no completion date is stipulated doesn't mean that the customer could wait forever to complete the purchase if they desired.
Also, a major point against the customer's argument is that the customer changed the terms of the purchase (that he couldn't buy until he sold his car) after the contract was entered into and the deposit was given. The customer's addition of the "deposit will be refunded" clause was likely made before he changed the terms of the contract by requiring his car to sold first.