How Do You Establish Credibility?

Credibility is establish my different factors such as doing what needs to be done, doing it in the time frame, with the quality and manner that is sought. If you say I can move a mountain then you need to establish that you can do the task in a manner that others expect you to perform. If you use a bunch of trucks and graders and tear the mountain down is that moving the mountain? Being able to complete a project with the given tools and restrictions or finding a viable alternative to accomplish the task in a more efficient manner will establish credibility. Telling the truth and being ethical in your actions are key factors.