If you get involved, please try to:

Be patient. Don't instantly blow off something someone says, especially a layman whose
interests or expertise may not be your own. Not all PhDs are true experts, and a lot of them are there from sheer inertia. I personally know a woman with a PhD in Sociaology who is barely literate, and of course there are lots of junk PhDs out there. And as Dan Rather discovered to his embarassment, some people are true experts in obscure fields, even without the magic letters after their names.

Listen closely to whatever evidence they give you. Watch the body language. People pick up on that and will tune you out even if what you're saying agrees with their own assessments.

Be pleasant & friendly. It'll help keep their guard down.

If you don't know or can't find an answer, say so. You will look better & people will want to hear more from you.

Never appear condescending, no matter how stupid the topic. You never know when a new discovery might show them to be correct.

Much of this advice comes from one of my former protegees, whose family works with stock & archival film footage. She is able to pinpoint when & where discussions collapse, simply from years of working with film.