It’s difficult. A downvote from an account with no history does nothing. Your bot has to post a lot of content first to attract upvotes from genuine accounts. Then once you’ve accumulated some rank, you can start giving upvotes or downvotes in bulk to the accounts you want to manipulate. It’s impossible to completely prevent that, but you have to do it a lot to have an impact.

I think this model is more resistant to trickery than it would seem, but it’s not completely resistant. I do expect some amount of trickery that will then need counter-trickery. On the other hand, the problem of tricking the system also exists in the current moderation model. You don’t have to outwit the system to get your content posted or ban your enemy if it’s trivial to flood the comment section with your content from alt accounts and drown them out instead. I don’t know for sure that something like that is happening, but it wouldn’t surprise me if that was one reason why there are so many obnoxiously vocal people.