Re PM: Right, a conduit or like an ECN, but it doesn't work perfectly. The line-up of MM bids/asks represent unsolicited orders from real customers. When there's none, they close. MM's juggle a few stocks simultaneously. Sometimes they forget and start making a market when they shouldn't. After a suspension, the system lets them slide in closing out any long or short positions.
NSS diehards should embrace greys and unsolicited pinkies because naked shorting is not allowed. LOLOL
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"We simply attempt to be fearful when others are greedy and to be greedy only when others are fearful."
-- Warren Buffett