MM's are institutionalized traders. They operate more like a clearing house for brokerages to front and cover most of the initial large trading expenses for buys and sells. They buy large amounts of shares in the OTC/pinkies/penny stocks/, and trade them for huge markups. PPS, in layman's terms, is short for price per share, which is just the market cap (value of the company) divided by the total amount of shares in circulation. It's a little more complicated than that, but that's good enough for you to get the idea.
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