In the A/E world, the phrase ‘expert witness’ (hereafter ‘Expert’) can bring to mind many thoughts. Some pleasant, some unpleasant, depending on the memory. Many of us have been involved in disputes where we thought the so-called Expert was anything but an expert. Perhaps their credentials were lacking. Possibly their investigation, which led to their Expert conclusions, was shoddy or incomplete. For whatever reason, their Expert opinion was wrong.
There are many well-respected Experts with excellent backgrounds resulting from their experience, education, judgment, and demeanor. That doesn’t mean the Expert cannot be wrong, they are human, like the rest of us, and are fallible. Some Experts will say almost anything their client wishes them to say, for the right price. These might be called Hired Guns, or even more derogatory epithets. There are those Experts whose opinions are not for sale. To paraphrase the late, great Yogi Berra, these Experts call 'em as they see 'em. Regardless of competency, many individuals make an excellent living from selling their expert witness services. Just do an internet search, and you will find thousands of Experts in any discipline.