I don't get any gripes or demands and frankly, after years in annoying corporate life, I just don't take on ANY client that appear to me as "difficult." There's a screening process beforehand, and they have the option to dislike me, as well.
Fortunately that's not happened. That's just a choice I have made in having my own business. People who are a pain in the azz can do that on their own time, and let me cook and be happy with my wonderful group of current customers.
Part of the PC process is sitting down with your clients and creating menus from a list of likes and dislikes that they have completed and discussed with the chef. In other words...every herb, every veg, every fruit and meat is checked off on a list. If they don't like basil, you needn't wonder "should I add basil". You know you aren't GOING to add basil or they'll kick your azz!
The best part of preventing headaches in this profession is to know the client inside and out. Cooking for people occasionally is not being a personal chef. That type of service falls more into a "Personal Catering" type category. Even in that case, all supplies must be purchased on day of service, and prepared in the clients' home. A Personal Chef is not allowed to store any foodstuffs in her own home firdge, nor cook on her own stove. Although some Personal chefs cook one-time dinnners for special occasions, a personal chef is basically a part of the family (live-out, of course. Live-in chefs, or chefs who cook for only ONE family are called "Private Chefs") who keeps solid records and files on their client tastes. Even with one-time service, they would still have to fill out the food questionnaires, for the major reason of food allergies! If I decided to make paella, and everyone is allergic to shrimp and clams, I have not only wasted my time, I have prepared a meal that will go to waste (as I am allergic to shrimp and clams!!)