Are you talking about theft (the provider stole the hobbyist's money) or robbery (the provider used force to steal the hobbyist's money and/or something else) ? My answer would depend on which.
For what it's worth, I was met by a provider with a knife. I gave her the money and went about my business. Not worth the effort for a couple of hundred bucks. Another reason to look at reviews.
It was not by force, she left with his wallet and cleaned out his bank account. I feel bad for him but I decided to stay out of it for various reasons.
We're talking about a felony then. If the hobbyist went to the cops and made a report, they would only be interested in the provider. LE cares a lot more about people stealing thousands of dollars by lifting a wallet with bank cards than a little flippy-floppy between consenting adults. Or he could hire a lawyer to make an anonymous report. Or he could make the report with an attorney in tow. But he should do something. Otherwise, he's partially responsible for what happens to all the future victims.