There’s always a way to get around these kinds of restrictions. But this is what the ‘Disclaimer ‘field is for. You input limitations (after agreeing them with the business owner) to prevent abuse.
In reality, it should not be a big deal because the intent of the coupon is to drive business to the store/café/shop.
It's a good idea to talk this out with your client fully. Remember to mention that if 100 people come in to buy a half price cookie, that’s 100 more cookies sold than the business would have (even at half price).