Help a desperate pensioner.

My mom was assisted by Hennie Brits. Such a selfish person. My mom just got her pension fund money and went to look for a bakkie from this dealership. Hennie advised my mom to put down the deposit of 20 000 without explaining the terms and conditions of the deposit. My mom got another car from another dealership and went back to cancel the deposit. He refused to refund her and said he will only refund us if we get him another customer who can buy the car. I mean how selfish is that? My 60 year old mom to get him customers . Then he went on to say that if my mom cancels the deposit agreement he will have to take 15 000 from the deposit and my mom will only get 5000 of her money. Any advice on the way forward with this matter?