[jfim]

If the buyers decide to hold their shares, then yes they could corner the market. I believe the broker could just elect to not pay the price and fail to deliver on the IOU. The SEC keeps a list of FTDs and publishes it twice a month [0].

If the shareholders decide to corner the market, the company could issue more shares or the SEC might step in and say "no you can't do that" to either the broker, the shareholders, or both.

I don't think the SEC looks very highly on people cornering the market, be it hedge funds colluding or individual investors colluding. The SEC is supposed to look for all investors, not just the ones that decided to corner the market in one security.

[0] https://www.sec.gov/data/foiadocsfailsdatahtm