You don't even actually match up buyers and sellers on the public markets anymore for stocks. Individuals (from retail to institutional investors) buy and sell

You don't even actually match up buyers and sellers on the public markets anymore for stocks. Individuals (from retail to institutional investors) buy and sell to market makers; later, when settling, market makers will pair up with brokers when clearing the funds. So it'd be up to the market makers to not fuck up and sell at $1. If not, it's their liability.