Of course its open to abuse, its open to abuse as things stand, just throwing it into the pot as a way to get a higher ratio of reviews per bookings as its been said its very low in reality. Probably tonnes of reviews on system already that were borne out of some ad hoc deal struck between both parties.
Its worth exploring some way for genuine escorts who want to be reviewed more in ratio to bookings. You could have a similar system such as ebay (no offense to anyone, just using as an example) where both the seller and purchaser of goods get rated as being on the level. So client A signs up as a gold member, say it costs 50 Euro a year but he gets 10 euro off every booking he makes via the pm system here so if he has 10 bookings a year then he has saved money but part of the deal is that he has to agree to leave a review within a day of booking date (not really much to ask) , if he does not do that then the escort can forward the pm to ad staff as proof of booking and his membership of gold club is revoked and the 10 euro she is down is taken from his 50 refunded to her via ad fee reduction and anything left over can be used to refund others via perhaps it being taken of an ad fee.
If he does review she has no say or control over if its good or bad and thats the chance she will have to take but as I say if an ebay type rating system then over time and with other escorts he saw adding to it his stock as a reviewer goes up and down accordingly...
Just an outline of an idea, nothing more, not saying its not open to misuse but lets get real people, anything to improve any aspect of punting will requie some sort of finacial incentive, nobody here are philanthropists.