Golden rules in my opinion
1. Apologise
2. Take responsibility
3. Thank them for the feedback; reassure that its welcomed as people often feel uncomfortable or anxious
4. Offer to rectify, replace or offer an alternative of their choice
5. Do not charge for said meal/s or replacement; this is a given and should not need to be asked for
6. May or may not offer something complimentary to the whole party; depends on the situation
Do all of the above gracefully, politely and sincerely.
There are some grey areas of course. Sometimes people make the wrong choice for them. It isn’t necessarily that there is anything wrong with the meal it’s just not for them. In these cases most people will acknowledge this and say so. It is really important that the waiter team knows the meals on the menu and the ingredients so they can help people make informed decisions. The menu presentation and written content is a vital tool to help achieve this and it should always be possible to adjust meals and accompaniments accordingly to accommodate people's preferences and allergies.
You can't please all of the people all of the time but no where is perfect and mistakes do happen, regrettable of course but we are all human; its how you treat and respond to people that will be remembered and what they will tell everyone they know.
We have implemented many changes over the years due to feedback from people; often minor things but these can make all the difference. Constructive feedback is to be welcomed and worth its weight in gold
This is just how we do things and not a comment or criticism on how or what others do.