You go to a gas station, kid is there, he wants a snack or magazine. Multiplied by the number of kids.
Charge at home and kid gets nothing.
There is a simple answer to that.
"I can just say no when the kid is unreasonable"
"My kid is not gonna have an iPad"
"My kid is gonna do his homework"
"My kid is gonna be polite"
What do you suppose parents have already tried?
Or did you mean don't have kids?
On the other hand if you continually indulge them then you can only expect one outcome.
There is a simple answer to that.