Would not take my Groupon. As I went to order, I mentioned the Groupon and the counter person pointed to a board that said they were not taking "Group Coupons" or gift certificates. He told me a previous manager set up those forms of payment and had the proceeds not go to the owners but to the manager. Good business management says you should not punish the customers for mistakes you make on personnel. If you want to run a successful business, own up to the mistake, make good on your liabilities if they were sold by someone employed and representing your business and leave the customer with a positive experience.
Edit: I just checked Groupon and as of 7/12/17, they are still selling for this restaurant! If you will not accept Groupons, make sure you discontinue your offerings on the website.