There is something about becoming an actor that many people never consider. You may have no talent, but you may have personality. You may not have good looks, but you have heart. Casting directors pick up on these things, so don't forget to make it a point to work on turning your "weaknesses" into strengths.
Talent casting can be a mean game. Some people are very cold-hearted and cut throat and they won't be concerned about hurting your feelings when they make a comment about your apparent lack of acting talent when you're at that next casting call.
The way to fight back is to steel yourself for any and all disparaging comments, but be open to constructive criticism. Remember that you're the one with the acting talent and they're the one sitting on their butt in a chair complaining about the amount of chocolate sprinkles on their cappuccino. Who cares what some feeb getting paid one thousand dollars a day whether he makes a piece of crap or not thinks about your acting? When did other people's opinions start to matter so much? Go into any casting situation in a fighting stance, prepared to show the strength of your talents, and block those low blows.