Misters are placed at grocery stores so as to mist groceries in order to keep them fresh.
Groceries lose water to the atmosphere by evapotranspiration.
The loss of water causes the cells of each of the products to go flaccid, giving them an overall wilting outlook.
What a mister does is spray the groceries with water at different intervals. The water coats the surfaces of the leaves and prevents evapotranspiration from the leaf surfaces from happening.
More on evapotranspiration can be found here: https://brainly.com/question/15401499