I am in St. Louis, am a self taught chef, caterer, and I use to run my own catering business, along with working as a personal chef. I would visit with the family to see what their budget was to make sure one they could afford me, and second, what the total cost of the project would be. If the total cost of an individual event was a set amount, I would let them know my fee would be 20-25 %. If it was a smaller gathering, the fee would be less. I never had anyone complain about the cost as I produced meals that were on par with many 5 star restaurants. I always shopped, prepped, cleaned up, and left enough for left overs. Flash forward, I am now 55 and am going back to working as a personal chef after working in restaurants, at home prepping meals for family, friends, parties. I can tell you nobody needs to go to the culinary institute unless they plan to work on a cruise ship. If your skills are honed after years of working in smaller venues, you certainly may work as a personal chef. I do not baby sit, change diapers, clean up after the kids, work as their nanny. You need to be clear with the family what you do, so they don't assume you are going to be their rug to be walked over.
If you are going to cater a larger event, let them know you will be hiring assistants so you can add that charge in as well. You want people who can take direction, do the work, help with clean up, and take down. If you need to hire servers, that is another charge. Don't nickel and dime them, but be realistic what you can do and what you know you will need help with. Lying is your worst enemy here.
If I ran into what some call difficult clients who at the last second changed their minds, I always had something in my back pocket I could prepare. But with that came an extra fee. I asked about allergies, who was vegan, vegetarian, etc. That gave me the enough to work with to know what I would be fixing, if they had issues with blood pressure, it meant dishes that could be made low salt without sacrificing flavor. You just need to know these issues come up, know how to deal with them and be prepared to do the work. I love to cook, so it was never that big a deal for me, but for some, they refuse to be flexible. You must be flexible in this line of work. If they ask for a specialty item like a decorated cake, I would ask them for how many, go from there, and let them know my fees would be less than a bakery cake, and better. But if it was a matter of time, and they wanted a decorated cake with the bells and whistles and time was a factor? I directed them to the best bakery in town. I would give the bakery a heads up they were coming so the bakers would know the budget, numbers, etc.
I lasted because despite my lack of culinary pedigree, I offered quality, price and dependability. I never had a client give me a bad reference. If you get one, my advice is go back and ask what they felt you lacked? Get specifics. One this is a learning curve and two, you can tell the next client , you have given that client a freebie, and yes you have to eat your fee to get back in their good graces, but do so. By then, what was a bad reference becomes a good one. I believe this is always worth it.