A business has to make money. How would you make money with this? Why would people pay you more then they would pay Petsmart, and then shipping on top of it?
Not trying to be mean. It's easy to think of things that we would like to do, it's harder to find ways to make money at it.
If you want to make money with fish, why not a betta boarding service? People with just one or two small pets (a betta, a hamster, a parakeet) often don't know what to do with them when they want to go away for the weekend.
Right now, most of my bettas are in 2G tanks - I can pick them up and carry them. You could board fish and little pets, anything that comes in a cage/tank, that's easy to carry. All you'd need was some know-how, a shelf, and a good sense of responsibility (and your parent's ok)