When will an expert not give an opinion whether a witness is telling the truth?

"The general rule is that an expert may not give an opinion whether a witness is telling the truth, for the determination of credibility is not a subject sufficiently beyond common experience that the expert's opinion would assist the trier of fact; in other words, the jury generally is as well equipped as the expert to discern whether a witness is being truthful." (People v. Coffman and Marlow (2004) 34 Cal.4th 1, 82.)