Rentmasseur.com has an option where you can report an user for fraud, abuse, scam or anything else. My friend is unsure if he should report or not. But he is very upset by the experience.
I agree with @AshburyGuy that it should not be reported. The reporting feature you refer to is not intended to report clients who try to get a “freebie.” I assume your friend would have provided at least a HE if the client had paid the additional rate. Your friend will likely encounter others who try for the same, so he should be prepared to address it and not get so upset about it.