When a deposit makes sense
For long treatments, new clients or busy moments. That's where an empty slot costs most.
Keep the amount reasonable
A deposit is a confirmation, not full payment. A small part of the price usually does it.
Say it clearly beforehand
State when booking that there is a deposit and what happens if someone cancels. Clarity prevents arguments.
Let them pay online
A client who books online pays the deposit straight away. You have nothing to follow up.
Refunding is always possible
If you have to refund a deposit, you do that from your calendar.