It's a rapidly changing marketplace. Based on what I've read, heard from Mistresses about no-shows early in this century, asking for deposits was a safe way for established dominas to make sure someone was serious about an appointment. That it has evolved into outright scamming online is not a surprise.
I've mentioned the following opinion either here, MF or the other site, namely that for me to send a deposit to a Mistress that I never met our tastes would have to be compatible. And a phone call would be important. If no phone call, I'd have to: check out her website & social media; read as many reviews of her as possible; and be comfortable with the amount of the deposit (and of course, the overall tribute).
I've only sent deposits to two Mistresses I knew very well, so well in fact that they gave me their business bank deposit number and real name, and I would go to the bank and make the deposits. (That's how I learned the appeal of serving a fin dom might be a turn-on. I'd text each Mistress after the deposits and, invariably both ladies would text me back with some suggestive remarks. LOL!)