Unwillingly paying customers is a difficult business to build, and they could go as far as making you do their work for them in advance before they pay you, sometimes, they never pay, and keep cooking up stories on why.

That's the problem of some businesses/services.

For example the price of an artistic work of art can be determined by the buyer. This is bad on the artiste who is bringing the service. Unwilling customers spells doom for a business or business person.