Some thoughts:
Why not drop the value of self-posts? Halve the value of them, or some other percentage?
Alternatively, could de-incentivize self-votes in other ways, like increasing their voting power costs exponentially with each one.
Or, once you are over a certain # of followers or SP, your self-votes do not count at all. The idea being that you now have a community enough to vote your posts and are less dependent on your own vote.
I like your second and third ideas -- subtle and effective!
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You have to take into account multi-accounting, so only the second idea would work if you would get lower rewards each time you upvote the same author in a certain time period (week?).
I've just published another idea on how to counter self-voting by de-incentivizing it. Read about it in my latest article Curation problems (incentive, rewards and self-voting).
Downvoting a post can decrease pending rewards and make it less visible. Common reasons:
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