From not too deep of an analysis, it would appear to be prevalent enough. It's a double edged sword in a way.
There is (and I have been swayed by this myself too) more credence (rightly or wrongly?) given to reviews left by more established clients. Escorts (and clients alike) are bound to be mindful of this.
Part of the game and possibly a necessary evil that we all benefit (and possibly loose in equal measure) from to varying degrees!