Remember, the 'customer' is always right. [=never argue with a customer]
He is one tough/tricky 'customer'. [=he is a tough/tricky person]
The company has good/poor 'customer' service.
(..) This is not about crossing lines. Which words Don't you understand? Look, if the whale was to bring in customers... Then we could spend some money on him. But since he's not, you're just gonna have to Make do (..)1993 Free Willy