Well yes if it requires another brokerage, but you can have trades if they can internalize an order at the same broker. Etrade for example has a lot of penny stock players, it is quite possible that there is a buyer and seller for this stock and Etrade is able to process that order.
However if you have 2 different brokers, as you said it requires a matched trade and the brokers have to use a process of external applications to find a buyer or seller.
Without Market Makers there is no liquidity and well as you can see, it is practically dead.
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