Buyer puts down a deposit on a car then backs out. Who gets the deposit?

I am selling a 98 Honda Civic, and I met with somebody to look at the car. They liked everything about it and decided to give me $150 to hold it until after the weekend when they would come pay the rest and transfer the title. They contacted me the next day, said they had a change in "financial plans" and would not be buying the car and included an address to return the money to. Within that time period I turned away close to 20 people who inquired about the car because according to the buyers who put down the deposit it was already theirs. My questions is I get to keep the $150 cash deposit correct? It is my understanding that the deposit is considered "good faith" money and thus subtracted from the overall price of the car when they buyers come to finalize the deal. If they don't come to finalize the deal, I keep the monies because of loss of business correct? Also, there was no contract or anything of that nature. Thanks