I purchased my first Betta (and first fish, ever) yesterday, before doing any research, and think he may be sick after reading more about them. I attached some pictures to illustrate what I'm talking about -- he's very pale in the body, the back of his tail/fin is tattered, and has these dark stripes on one side. He's eating fine and swimming around, so perhaps it's nothing.
I bought him at PetSmart where they have dozens stacked in little tiny tubs swimming in their own junk.
NOTE: Ignore the tank, after doing some reading I went and bought a 5 gallon with a filter, heater, things to put in it.