Another way to see a no reviews policy that is from a less suspicious perspective, is that the provider may be very good and not feel reviews add benefit.
Depending on how reviews are written or how busy a provider already is, positive reviews can have a negative effect in who they attract.
I remember in the very beginning of working as a sw I got a positive review that was uncomfortably graphic. I found it really challenging to read, first of all. And yes, it did result in an increase of requests but it was not at all the types of clients I was looking for or enjoyed meeting. Reviews can also result in people's imagination creating expectations that a provider isn't interested in fulfilling or hasn't promised.
I know there are some who will laugh as usual but a super graphic, detailed review of yourself, even if positive, can actually be almost traumatizing to read. And some providers get review after review after review.. Imagine a negative one from a person you just didn't connect with or who was a jerk but obviously doesn't say so in his review?
Tasteful, discreet reviews are not so bad but maybe some providers would rather not take the risk of their business is doing just fine already. If you consider it from that perspective, there's nothing suspicious about not allowing reviews. I can totally understand why someone would choose that and I appreciate the fact that Merb respects that.
It's your call to avoid someone who doesn't allow reviews but this is something she's already considered, accepted as a possibility, yet still chose not to allow.