NSAV Holding Inc (NSAV)

[shotsky]

Spreads change all the time. That's how you know each MM's demand. If you sell into the spread, they have to buy your shares. If they get an excess, they may change the spread to quit accumulating. Or, if they NEED shares to fill an order, they may change their bid to get them faster.
Lastly, if they don't have enough, but can find them for sale at any price, they can borrow (not buy) them and replace them later. Technically, it is shorting, but that's not why they do it and they virtually always close out by end of day. They do it because their income is solely based on their spread, and filling an order with borrowed shares works to give them the commissions.