When one sees that there are some discrepancies or deviations, the best way that he can serve that person is by pointing out the fault. By doing so in the mood of service, it is a lot easier for somebody to accept it. However, if he points it out in the mood of malice or envy, then the statement may not have the same effect.
Lectures from a Disciple, "Vaisnava Etiquette", Pg 326,5th Paragraph