Joseph,
How can we identify the modern-day eruv rav
1. The eruv rav may sometimes be seen along the edges of a frum community on Fridays.
2. If a particular rav declares “down!” on Friday before Shabbos, and then nobody carries anything outside on Shabbos, you’ve found your man.
and how should they be dealt with?
I think they like donations. Eruv repairs can be costly.