I've said it before and I'll say it again. Paying a deposit is a mug's game.
When you're told a deposit "guarantees" or "secures" your booking, that just isn't true. It's just wording to play on your confidence in them being trustworthy. All a deposit guarantees is that they have your money - don't kid yourself in thinking it guarantees any more than that whether it's your 1st or 21st time.
Even when you're seeing a legitimate escort, that still applies. They just honour the agreement like any honest person would.