And if you've announced to everyone they can't buy anything on day 15, they're just going to buy things on the 14th or 16th. The business still gets their money. The increased sales before and after the boycott day can easily make up for that boycott day
The daily sales goal is not as important as the weekly, monthly, quarterly, or yearly goals. You need to make them miss at least one monthly sales goal if you want them to even pay attention.