That's exactly what they do. Only sure way to know if a trade on the bid is a buy, is if it's your buy, same with sells on the offer. Too bad MM sales reports are no longer available, they were great to have years ago for the BB's, first they were free, then $15/day, then POOF, no longer available.
Now all you can get is MM total activity by the month which is interesting but mostly meaningless.
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