I don't know about the stores you reference, but there are many many shops in my area where there might be three girls, and one is a superstar, while the others are meh or maybe above average but far far below the star. Reviews flow from that. Is one called Massage Marvels, they have two or three girls at any time, and while one is a 10+ and nice as can be, the others are far far less, and their reviews count and result are commensurate. Or Green Spa Plus, there is Tina, and then reviews for the other girls are basically non-existent. The girls exist, and I guess people see them because is often that store you have to wait your turn to get in, but hell if I see five reviews a year for the other girls, total.
For me, if a shop has several girls but there is only one who is a champion and the others are average or less, I never go there. I don't make appointment, I'm walk-in only, and am no going to get the lesser girls or wait around for the top one. Too many other awesome options to wait in line. And I only write a review on average every ten or so visits, doesn't mean I'm shilling those girls, it's just those specific visits warranted sharing the intel. Am no going to write a review for generic Chinese lady who gives generic service and I left averagely happy. I write review when girl or shop is fucked up or when menu changes or when new girl is awesome and my pals need to know that this shop is no shitty anymore or whatever. Can be any of these items.
Real shilling is as
@User826 says, when one guy says a girl is a slamming 10 or 11 and does BBanal for ten bucks, while the forty other reviews say therapeutic only and she's an ugly lady who uses her elbows.