Chiming in here...
“The first lesson of economics is scarcity: There is never enough of anything to satisfy all those who want it.” — Thomas Sowell
The only portion of our business where we never run out of food is the Catering side. Onsite catering at a Wedding reception, Birthday, Corporate Event - Running out of food is unexcuseable, and can be the kiss of death for your business. We only take one Catering event per day, and concentrate on that event. Our Food Trucks and Restaurant were another story.
Trucks were a different story - We could only stock so much product, and hold it for so long, so we balanced our pricing with how much we had to sell, over how long we could sell it. A typical truck "stop" was 4-5 hours, and we typically sold out in 3-4. Our customers knew we had the best food, at a reasonable price, and to get there early to get it. This was the case for 2.5 plus years.
At our Restaurant, we made what we made each day, and very close to contest quality BBQ. We had certain specials on certain days/eves, and when we ran out, we ran out. Burnt Ends on Fridays were usually sold out by 5:30 for example. Never had anyone bent outta shape because we were out of a certain item, the comment was "Wow, that must be really good. We'll get here earlier next time". We structured the operation around what we knew we could do really well each day, and charged accordingly.
That said, all this took time and we made plenty of mistakes along the way - lol! I think the idea of "The Customer is King", and "Always Right" can be problematic. I've always said "The Customer is always the Customer" - We've always treated them with respect and hospitality, and made some nice frends along the way. Business is different now, more regulation, costs, pressure, and moving parts (Social Media, Internet, Email, etc). He'll figure out where he needs to be, and find his "lane". Success takes time, and nothing feels better.