He deals with the customers in a very 'professional' way. = He is very 'professional' in dealing with the customers.
a golf/tennis 'professional' [=a skillful golf/tennis player whose job is to teach other people how to play]
I was impressed by the calm and 'professional' way she handled the crisis.
(..) What in the world... Oh! I thought I told him to pick these up. Shouldn't they be there by now? What's taking them so long? Hey, these guys are professionals. They're the best. Come on! They're not lying down on the job. Go on without me! Just go! (..)1995 Toy Story