Hi, the practice of taking a deposit is not good practice.
The garage is not selling you the car so there is no contract of sale to you personally, the car is the object of sale to motability as they are the owners not you.
The only time a deposit is payable would be for any extras you personally have ordered.
The offer and acceptance of the car takes place when and as you enter the Pin number, also this starts your contract with Motability and not with the garage.
Suggest you contact Motability and complain about the practice Good luck, Mike