I don't have a brick and mortar store so my experience is a bit different. That being said, I've probably "fired" more customers since 1979 than anybody else I know of.
Simply, like you, I'm doing the best I can. Problem? If it's easily fixable, I fix it. If it's not (sorry you don't like Hershey's syrup-but that's what we have) I give them a refund, a quick apology, and suggest they try another place.
Here's an example. I have concession trailers. EVERYBODY is an authority on how a fountain soft drink is supposed to taste. Too sweet, not sweet enough, not carbonated enough, etc. etc. There are a myriad of reasons that my soda won't match what is in a bottle or can. Most common is the local water. If I'm at an event that serves off a well, the soda will have a mineral taste to varying degrees. If the water is soft, then the soda won't be as carbonated. If I'm a long way from the water source on a hot summer day, the water entering my system will be hotter than usual, and this also affects the finished product. That's the background.
Somebody buys a Coke (for instance) and doesn't like the taste. I offer another flavor soda. They don't like that. At that point I give a refund, apologize and try to move on to the next customer. What I don't do is give another soda and another soda (well let me try the Sprite. Let me try the root beer. Let me try....) I explain that the soda all uses the same water and the same problem will probably occur again. Customer has their money back, it should be the end of the story. Sometimes it isn't.
Sometimes people just do not want to accept that you've reached the end of your ability to accommodate them. I have refused to go further, and even had customers bring in the police. "HE HAS TO SERVE ME!" Of course the police have to break it to the customer that I don't, and etc. etc.
You're not going to make your livelihood off of one person. You have to focus on the greater number of customers. Staff is increasingly harder to attract and retain, and if you have an abusive customer who is stressing your people out, it's a simple calculation as to which is more essential to your business succeeding.
As far as a customer bringing in their own syrup or condiments? Pretty tacky, but I wouldn't give a darn as long as they didn't go table to table bad mouthing me for not offering something they wanted.
One of my trailers is a pizza trailer. People ask for ranch dressing from time to time. It's an abomination in my opinion, but I will buy PC's and I sell them at a premium price. It is not convenient for me to have and I expect to be rewarded for making this available. When I hear "I don't want to pay $2 for a cup of ranch" or "I can't eat pizza without ranch" I ask them why they are not carrying a small bottle with them. If it's that important....
I would stick to my guns, wish this guy a good life and go on and thrive without him.
