I did an advanced forensics course a few years back that was geared towards preparing me for court cases for the company I was working for. I quickly realized how easily "expert" witnesses could and most likely were being abused in the system just as you say. Expert shop till you get what you want.

That's not even mentioning the epic level of incompetence I saw among others. I'm talking about "forensic experts" who didn't know any filesystem other than NTFS, and even then if the tool didn't do it for them they didn't see it... At least I know if I ever end up defending myself I have plenty of inside knowledge on how to undermine the prosecutors arguments.