Credibility is the quality or power of inspiring belief or trustworthiness. In the professional world, a person's or company's credibility often determines success or failure.  Today, credibility online has become an important topic.
Build your credibility before persuading.
American credibility in the war on terrorism depends on a strong stand against all terrorist acts, whether committed by foe or friend. -- Arlen Specter.
Synonyms: reliability, plausible, likely, reasonable, tenable.
Antonyms: incredibility, implausibility, improbability, unreasonableness.
Factors Impacting Credibility
Credibility-enhancing actions include: Showing you care about the other person and have their best interests at heart. 
Language that reduces credibility includes: Totally and absolutely excessive exaggeration. Ibidem
Whitehead, J.L. (1968) identified expertise, dynamism, and trustworthiness as factors impacting credibility; other key factors that impact credibility include: age, gender, country of origin, and education and income levels. 
Establishing credibility includes:
- Being honest is more than telling the truth. Hidden agendas and withheld information compromise your honesty even if everything you say is true.
- Follow through with promises.
- Back up your words.
- Maintain confidentiality. 
Objectivity and Credibility
Be objective and specific and support what you say with evidence, such as facts, statistics or testimonials. Be even-handed; If you are presenting possibilities, give all options a fair hearing and don’t leave out important information. If your reader finds out you’ve omitted key facts, you’ll lose credibility.
|“||The merits of each evaluation role will be discussed as to its relationship with credibility, objectivity, independence and usefulness.||”|
Components of witness credibility are:
- Dynamism