6. Acting Skills
Sometimes you're going to come across people that you'll never be able to make happy.
Situations outside of your control (they had a terrible day, or they are just a natural-born complainer) will sometimes creep into your usual support routine, and you'll be greeted with those "barnacle" customers that seem to want nothing else but to pull you down.
Every great customer service rep will have those basic acting skills necessary to maintain their usual cheery persona in spite of dealing with people who may be just plain grumpy.