Thanks for the answer. It would be possible to program the bot that it can find out who paid for the upvote because the mechanism always works the same way:
any user sends amount + a link to bot -> bot upvotes the article behind that link
So, you have to check wallet memos if the link of the articles appears in any of them. Of course, this would leave open two potential backdoor: 1) Unknown 2nd accounts and 2) URL shortener.
When it comes to complaints for retroactive unvoting simply refer to the rules. They are the same for everyone.
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it couldn't find out when utopian vote first before the user buy a vote. that should be the case. @doodlebear