"Expert witnesses" are a dime a dozen.
In the United States, it is possible to drag someone off the streets and certify him/her as an "expert witness" without any deep qualifications. I can get an "expert witness" to argue that the earth is flat. Hell, I can be an expert witness. In the US, the onus is on the Judge is to decide if they are qualified to be an "expert". Unfortunately, the judges typically do not do their homework to determine if the person is following the generally acceptable scientific consensus.