They don't know for sure since BMIC, like the rest

They don't know for sure since BMIC, like the rest of the MMs, have client accounts as well as their own accounts. They can see who's bidding/asking what by the L2. You can see some of that detail on the OTCMarkets web site for stocks where they've enabled it. RMHB is visible, so you can see if one of the MM's is maintaining a "wall" or an ask low enough with enough shares available that it holds the price down, hence the term "wall". They are in the game to make money just like the rest of the stock traders, and that's what they do. At some point, not far off I believe, the buying pressure will push through their wall(s) and they'll be forced to work in a higher support range.