Although technically, an expert is told that he must serve the interests of justice by assisting the court in reaching the truth, and not blindly support the party that hired him, it cannot be denied that most of the time, an expert will be extensively coached on how to answer tough cross-examination questions and skillfully avoid statements that will hurt the party that hired him.
http://www.slaw.ca/2014/02/11/the-future-of-expert-shopping/