If the Job Is Not Right for You, the Professional

If the job is not right for you, the professional way to turn down the offer is:

A) immediately, or as soon as possible, so as not to waste anyone's time.
B) by contacting the employer by phone, if possible, then following up in writing and thank them for the offer.
C) by simply sending a brief email saying thank you, but you are not interested at this time.