Your example is silly... No one will have a >90%+ win rate for a significant number of games, followed by a <10% win rate for another significant number of games (significant number being enough games to gain/lose a few thousand mmr) when they magically start playing from another IP. Streaks might happen over 10-20 games, but we're talking about detecting boosters and account buyers here, so we're talking about gaining/losing thousands of mmr immediately following a curious change in location. Obviously the smaller the number of mmr that is boosted, the more difficult the boosting will be to detect using some kind of algorithm, but for the kind of cases described in the OP...It really would be trivial to detect this sort of thing. Like some kid could figure this out as a high school project kind of trivial...

It's funny how everyone is acting like the 90% success rate means 10% false positives.. No, it would be 10% of borderline cases fall through the cracks, but 90% of situations which are more obvious and easier to detect automatically, would be detected... So it would be unambiguously better than what we have now. The reason the success rate would be 90% and not 100% is to prevent false positives from happening so where this idea that 90%=>10% false positives comes from, I really do not know...