May I make a suggestion as being in the business so to speak it might help.
If you know the food can be good or not as the case might be, or the service one day is great and the other isn’t. Simply go in when they are not busy, see the owner or manager, state your concerns and ask to be looked after to the best of their ability. Make the reservation for when the person you speak to will be there so it’s fresh in his or her mind and also ask for the server of your choice or the best that they have. It usually works and if it doesn’t nothing else will.