If somebody votes on too many posts by the same user within a certain time period, we should display a popup like this:
You have voted on too many posts by this user in a short time period. Serial voting could result in a vote reversal and you may get your account suspended if you continue doing it.
Do you really want to cast this vote?
[Yes] [No]
This would openly reveal the algorithms used to detect serial voting.
Serial voting isn't a problem that only exists if you hit X votes but not X-1 votes. We don't know exactly the algorithm works, but imagine it was 10 votes on a single user in a week: if it warned you when you were about to do vote number 10, then anyone who wanted to manipulate votes in this way would just stop, and wait a few days until the popup stopped being shown to them. But just because they stopped doesn't mean that their other votes were good ones. The algorithm should remain hidden so that problem users will demonstrate their problematic behaviours.
The parameters of serial-vote detection are intentionally kept private. The last thing we want to do is to tell people who intentionally engage in this behavior how to avoid detection.
A warning like this, if always accurate, provides useful data that people can use in experiments to work out the parameters, all while going undetected. In contrast, actually tripping the script leaves a record, which moderators can look at when deciding what corrective actions to take.
A softer reminder could be ok if supported in the feature request. Low-rep users get some reminders like "remember to vote on questions" and "remember you can accept this answer"; possibly something could be done for voting too, specifically for low-rep users. I don't have a specific idea in mind and am not convinced it's needed, but that might be something for you to think more about.
