I was thinking about that too, there is also the "mimimum mark up" law here in Wisconsin. So, one count each agaist those who knowingly stole gas, and two counts against her. ;~D
Let's think for a second about the .0001% who actually might have needed gas. Minocqua's a pretty small town, and although I didn't count the number of service stations last time I was there, it surely can't be many. And patrons shouldn't be expected to sit out overnight to wait for the error to be corrected.
I would guess that the first person to receive the "discount" probably was there not to defraud but just to fill up. Their poor form was in notifying everyone else of the error; in a community such as Minocqua, you would think they would have the class to notify the owner instead.