Being credible is simply the perception of being trustworthy and believable. One of the key reasons is that the brand represents a level of quality that they know and trust. A key factor is being consistent.
People are more likely to trust a business or person who acts in a similar manner most of the time.
For example, if your publish a newsletter to your customers or potential clients, aim for similar quality in each issue. Also, be consistent in your style of writing. Publish on a regular basis - irregular publication schedules cause confusion in the minds of your readers. C onsistency applies to every aspect of your business. Don't change your guarantee terms every couple of weeks.