Witnesses are truthful and trustworthy, fair and unbiased; or they are not; they are reasonable and consistent in their statements or the contrary; their opportunities for seeing and knowing the matters and things they testify to are favorable or unfavorable; they may be interested in the result of the trial or they may not be; and they may be impeached or sustained. All these matters relating to the witnesses are collateral issues to be determined by the jury.

The jury are not only the sole judges of the facts and weight of the evidence,68 but also of the credibility of the witnesses.69 And when there is a conflict in the testimony of the witnesses the jury must determine to whom they will give credence.70

But when the competency of a witness is in dispute, the question is one primarily to be decided by the court.71