I noticed this, then someone I know irl brought up somethin quite eye opening.
So, my native fruit is grapes, and I put all my stuff dirt cheap. I try to keep grapes in my box stocked. I'm the only one in the house who has grapes, the other 2 are lychees. Since grapes are their not native fruit, they can buy my dirt cheap grapes, sell them OUT OF THEIR POCKET and make a profit. People are making a profit from their pockets by buying dirt cheap not their local fruit and reselling it.
I'm a salty person, the kind who doesn't like when one person will raid my entire box. So the fact that they will buy my grapes, then sell for profit, when someone else could use them to give to an animal? Not having it. This is why I now make my grapes as high as they can be. Plus bells are so unnecessary, but it's really to prevent people making a profit off of them.