The £99 reservation is a holding fee, not a deposit. Auto Trader will always give you the money back, even if you decide not to go ahead for any reason.
After the reservation is made, a deposit is sometimes requested by the dealer. This is not a fixed amount and can vary depending on the car and the dealership's terms.
The deposit amount is separate from the £99 reservation fee.
Find out how you can get your £99 reservation fee here
If you have any questions about deposits, please contact the dealership.