Yet they have no clue what they did or why they are banned. They asked me and I looked but saw nothing of any note that was problematic.
I'm curious if anyone has any idea if there is another step they can take to resolve this amicably or if they just need to accept that they are permanently banned and have no recourse or reason why.
from what you describe (they are not tech savvy, and when you looked everything was fine), it sounds like the site was compromised at some point. It could be compromised now, but maybe only shows the hacked content (with counterfeit goods) to certain visitors (e.g. normal content when you type the address directly and hacked version when the referrer is Google search or ad). This is a common technique so that the site owner doesn't see the hack.
Alas, every submission to the "appeals" form comes back with identical, seemingly-automated responses, and my Adwords onboarding specialist has yet to receive a response internally after a month of followups