I would be surprised if any concierges did not get kick back. However I would hope that they would only send clients to places that fit the need of the paying customer. Most of the time the reccomendations are good.

This is dependant on local variables however. Concierges in Italy for example, seem particulary in league with the local mafiosa and intent on aiding the process of helping to ripp off visitors and protecting local scams. The Excelsior in Naples whilst being a truly great hotel suffers badly from this.