I'm a professional and I have to conduct myself in a professional manner.

我是专业人士，必须以专业方式行事。

《柯林斯英汉双解大词典》

It is of the utmost importance to answer the phone in a professional manner.

以一种职业化的态度和方式接听商务电话在职场上是非常重要的。

youdao

Attend to all guest enquiries and complaints in a helpful and professional manner.

用乐意和专业的态度对待客人所有的问询和投诉。

youdao

The ads have an amateurish feel, albeit that the amateurishness is executed in a totally professional manner.

BBC: Magazine

"Generally, our employees are acting in a professional manner, but every so often there may be a burst of anger, " he says.

WSJ: For Businesses, Bully Lawsuits May Pose New Threat

But if you take the time to communicate in a professional manner, you will gain the respect of the employer whose offer you rejected.

FORBES: Decline a Job Offer -- The Right Way!