Reputation
The first criterion of credibility is reputation.
Sometimes we have a good idea whether or not a witness is going to be reliable, even before we look at the details of their testimony or the situation, simply based on their reputation. Other things being equal, a good reputation makes someone a more credible witness, while a bad reputation makes a witness less credible.
Reputation can be broken down into two parts: status and track-record.
Status
First, consider the impact of status on a witnesses credibility. If someone is in a position of responsibility, then this reflects well on them. Professionals such as teachers, lawyers, or doctors are considered to derive credibility from their professional status. If they weren’t trustworthy, then it is less likely that they would have been able to make it in their profession.
Status can also be boosted by recognition. If someone wins an award for the quality of their work, or has a title bestowed upon them, then this is a positive sign.
Conversely, someone with a bad reputation is less credible. Rightly or wrongly, used-car salesmen, estate agents, and politicians are generally regarded as slippery customers, as people not to be trusted.
Track-Record
Second, someone’s track-record can also affect the level of trust that we are willing to put in them. If we know that someone has told lies in the past, then we will be less trusting of them in future. If, on the other hand, we have long experience suggesting that a person is reliable, then we will be more inclined to believe them.