George's Employment blog has this post that includes a useful catalog of an ALJ's explanation of his credibility findings in a case under the NLRA. Check it out.
In at least one NLRA case with which I am familiar, the ALJ listened to the head man for the employer and determined that his testimony was so untrustworthy, whatever he said would support an inference that the opposite was true, even in the absence of any other evidence on point.
This conclusion has always boggled my mind, these many years, but it seems to describe what often happens in litigation - the most demonstrable and offensive liars often lose, whether or not they deserve it. Two famous examples are the O.J. Simpson criminal and civil trials. In the civil case, O.J. was impeached most obviously by the photographs showing him wearing the shoes he denied ever owning, even the shoes were not the most important evidence; in the criminal case, law enforcement despite all the blood evidence was impeached by the Fuhrman tapes, etc.
A question I have sometimes heard in trials and even asked a time or two myself is this: "Mr. Witness, are you as sure about this as you are about everything else you've said in this case" - meaning, you have just told us a magnificently transparent whopper of a lie, which ought to taint every other word you've said today.