Food comping should only be used in extreme cases. By comping food, you train your customers to expect it. Then when you don’t, they’re dissapointed for not getting something they wouldn’t have gotten at another restaurant anyways.
A customer that simply orders something they end up not liking, not because it was bad, but because it doesn’t suit their taste, is never someone whose meal should be comped in my opinion. Along with other complaints from customers who eat most or all their meal, or do not have enough of an appetite to let you make them something else, you should be offering these people some sort of bounce back offer instead of a comp.
Your first approach should always be to try and replace the food with something they do like. Even if you have to make a dish twice, as long as you collect the money for it, you still have some gross profit left to contribute. When you give a comp, you not only don’t get the money, but you also incurred the expense of preparing the food. The difference between collecting a reduced gross profit, and actually paying your customer to eat with you is huge.
If you can’t replace the food, and the customer’s complaint is reasonable, offer them a coupon or gift certificate and promise to make their next visit better. By comping the meal, you can’t guarantee that the customer will even come back. When you give them a discount for their next visit instead of a comp, there is a very good chance they will return, and they likely won’t be alone. You’ll have the opportunity to make a better impression and win a regular customer.