Some studios ask for a deposit when you book. It is normally a percentage of the service or a fixed amount, and it comes off what you owe at the appointment — it is not an extra charge.
Deposits exist because an empty chair costs an independent professional the whole hour. A studio that takes deposits is usually one that has been let down often enough to need them.
Whether there is a deposit, how much it is, and whether it is refundable are all set by the studio, not by us. Those terms are shown before you confirm, and they are the studio's to explain. If you are unsure, message them before booking rather than after.