So called "expert witness" testimony has little value when the either the plaintiff or the defendant provides the "expert". They could be getting paid to testify in which case they will say whatever the person paying them wants them to say.
kid, go see some court hearing related movies or something.
All a competent attorney has to do is ask them if they are being paid to appear in court and that will cast doubt in the minds of any jury. Not only have I seen movies, I've served on juries. How about you? And I'm no kid. I'm probably old enough to be your father.