Using coops to send resources to my own account would have been pushing, a ban-able offense. I got coins by being insanely active and farming, farming, farming... And then more farming (followed by farming).
Co-op as it exists now is TERRIBLE for the late game. There needs to be a 30-day limit that requires the original player to log in to reset the timer, where if the original player doesn't log in, the coop is removed and the account gets turned into barbs. That would free players from having to manage accounts of people that quit, and force people to internal quickly. I would love changes to coop.