You may want to consider the cat after the mice are gone. The reason is that you don’t want the cat bringing dead mice to customers as a gift. Cats are thoughtful that way, and humans are just scared by it because it’s death.

I suggest finding where they’re coming in, it has to be from somewhere, and close that off.

For the candy bars, put them in a fridge or a cooler, in either case the mice can’t get in. Chances are that without food, you’ll have no mice. If there’s no reward for them, there’s no reason to be there, there’ll be food elsewhere.

Also I’m not sure but I think if you can find skunk spray and spray it outdoors it might help. Skunk spray is a spray that has the chemicals that skunks emit, so it basically is the smell of death. Most animals, and humans dislike the smell, so it can be an easy way to deter them, not sure if it’ll work though.

Anyways though, basically sounds like your mice are coming around at night, because you didn’t comment on customers running about screaming. So they’re coming out when it’s safe, sneaking some food.

So the first order of business is to put away the food, hide it in a fridge or a cooler. Second order of business is to track down where they’re coming in and seal it.

But you’ll likely find that with no reward, they’ll feel no need to come inside, they’ll just move on.

How about adopting a store cat?

I agree with the CAT method. Most customers won’t mind a cat being there, cats are generally neat, and they are independent so they won’t care if you leave them there at night.

Mice are quite smart and resourceful. And unfortunately, reproduce quickly. The easy answer is to get an exterminator.
Other, less expensive methods are available as well. First you need to find out where the mice run and feed. Since they urinate constantly and they like to run along walls, look for grease marks and small droppings. A black light will show you their urine trail. Once you find their trail, get a toilet paper tube and crease two lines to form a flat sided tunnel. Put a treat on one end of the tube: A cracker and dab of peanut butter works great.They will eat the peanut butter as soon as they’re sure it’s not a trap. Now comes the easy (mouse-friendly) part.
Get a tall (at least 20 inches) bucket. A trash can works well.
Balance the tube precariously on the edge of a table or counter with the treat hanging directly over the tall sided receptacle.
The mouse will scurry to the treat (they like tunnels) and fall into the trap.
Set the fella loose at least a mile away from your abode.
Good luck

a cat. just went to a bookstore and they had a cat.