The best part of the fediverse is that anyone can run their own server. The downside of this is that anyone can easily create hordes of fake accounts, as I will now demonstrate.
Fighting fake accounts is hard and most implementations do not currently have an effective way of filtering out fake accounts. I’m sure that the developers will step in if this becomes a bigger problem. Until then, remember that votes are just a number.
Maybe instances should be assigned a rank for how dependable they are. Length of time active, number of active users… Stuff like that and each instance keeps track of its own rankings for each instance it is federated with. Put the upvote and those stats in a magic box to calculate the actual upvote value.