They can only "game" the system if they create paid accounts with friends CC, as you say that's impossible to do with hundreds of reviews.
On a good trip an escort is usually busier than back home, therefore he could get multiple reviews within a few days and after that no reviews for a while, also if the same guy reviews an escort is because he's a regular.
I know an escort who has over 300 reviews and still guys ask him if he's a cop... He had 2 negative reviews that were later removed, and potential clients constantly asked him about them: "what went wrong?", etc. To some folks nobody is good enough!