Agreed, being able to become part of any group makes this problematic. Without repercussions, it seems difficult. Detection of ownership and the following loss of trust seems to be also in order. Or make the trust innate, not sellable to others, under the assumption that you cannot sell yourself.

Otherwise, it seems really like a cat and mouse game. Another option may be to force SEO to be indistinguishable from the best content. Is that the current goal?