We source live secondary market data from the market leader, Caplight, that institutional investors use to monitor secondary market prices.
Given how thinly traded private stocks are, you should use this data as a helpful tool, but not an ironclad price and nowhere near as reliable an indicator as publicly traded stock prices. Closed trades are much more useful data points than individual bids and asks, as a bid or ask is just what one person is offering to buy or sell shares at.
Keep in mind that you may have transfer restrictions on your shares, so a tender offer may be your best opportunity to sell your equity. You can learn more about selling on the secondary market in our Sales & Loans Guide.