He should identify if other accounts are paid by MB or SS to upvote a post. He tracks all incoming transaction to these vote selling services. So if someone sends - let's say - 1 SBD and the post link as a memo to MB, will track this purchase of votes and discount the reward accordingly.
Maybe I didn't really get what you mean, but does this answer your question?
RE: Here is how the Steemit Trending Page would look like without Bid Bots and Self Votes! (23.06.2018)