Do you know pet turtle under 4-inch long is illegal for sale in the United States? The ban has been in place since 1975.
The reason is quite simple, turtle of all sizes might carry salmonella.
The easiest way to get it is to put a turtle in your mouth. Unfortunately, it is something small children might do often.
The 4" size was chosen because anything bigger would be harder to put into your mouth.
Every turtle owner must know about salmonella. Wash your hands after handled your pet turtle can help. You may also use Disposable Gripper Sleeves.
I guess if you have a small turtle and you want to sell it, you probably have to wait until it's bigger lol. Not exactly a solution if the species isn't going to grow bigger than 4".