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Creating a ton of sock accounts would requires vastly more effort and time than an auto-vote bot, unless I'm mistaken. That's a disincentive to pursuing that particular course of action, especially given that new accounts have practically no weight at all.

Wouldn't it necessitate only one sock puppet account. It could be seen negatively to upvote its own comment this way but it still could be done.

At this point I tend to disagree with this solution and I'm still unsure about the course of actions that should be taken.

I agree with @teamsteem, the creation of just one sock-puppet account is an almost negligibly small discomfort to the average (ab)user. That's why my own algorithms have always treated self-votes and sock-puppet-votes the same.