The stock market is not all public. Stocks can be sold privately, (i.e. private contracts, stock bartering) or trading private collaterizable assets (i.e stocks

The stock market is not all public. Stocks can be sold privately, (i.e. private contracts, stock bartering) or trading private collaterizable assets (i.e stocks in private companies). What you see on CNBC is the average buying price what people are willing to purchase on the public market. How do you go about valuing those transactions?