The legal obligation of an expert witness is to provide independent advice to the court by presenting impartial, unbiased opinions about matters within their field of expertise. This duty is owed singularly to the court and supersedes any duty to the attorney or litigants. Your job, as the attorney, is to find the right expert for each case. One size does not fit all.
Kleinman, Toby and Pollack, Daniel. (November 18, 2019). How To Select an Expert in a Custody Case. New York Law Journal.
*This is constructed from limited available data and may be imprecise.