Yes, 4 devices in a row. You are proof that can happen.
Sorry, my experience with pawn shops does not match with what you are saying. My research says they do knowingly take in stolen property from know thieves. And don't even get me started on Gold and Silver shops.
You need to get your 9,000 members together and go public and get the public to get behind you in your fight. I'm sure they will see your plight and decide that antitheft tactics are unimportant we need to insure that pawnshops and used phone traders don't lose money.
I've been in an AT&T store when someone is trading in their iPhone. Before they can do so the employee has the "seller" turn off Find My iPhone, iMessage, iCloud, and remove their email account. They do seem to be knowledgable in this regard. Not surprising really.
You could call Apple and plead your case with them. Call AppleCare and ask to be transferred to Customer Service. Keep going up in the chain until you reach some sort of accommodation.