Things that you have to do as an expert
1/State facts as they are not by the one who pays for your services.
2/ Do not be too technical but state facts
3/ do not use generalizations.
4/do not make statements that are untrue and mix with truths as this is unethical.
5/do not be emotional or get involved..
6/ say it as it is.
7/when you are wrong admit it.
8/examine the material with dexterity for falsities