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.
(..) You better shit-can that blasphemy, boy. You're in a house of worship. Sorry, Pop. Well, this is definitely the work of professionals. I'd guesstimate Mexican Mafia hit squad. Four, maybe five strong. How can you tell? Well, a sure and steady hand (..)2003 Kill Bill: Vol. 1
(..) It's a primitive culture. I'm just trying to blend in. He didn't believe our cover story. We're running out of time. Will he be able to handle the truth? If you're looking for my professional opinion... He's nuts. I'll be sure to note that in my log. Captain, I believe I'm feeling... anxiety. (..)1996 Star Trek: First Contact
(..) Completely focused on her work like a lot of athletes that I work with. Really? How about you? Are you focused on her? I am totally professional. I don't sell dope, and I don't hit on my clients. Okay, well, we're gonna take a look around. Be my guest. (..)2015 TvShow: Bones Title: The Promise in the Palace Season: 11 Episode 7