No, because not every potential buyer can or will participate, so by limiting the customer base the seller is limiting the price. "The market" is bigger than those auctions for a variety of reasons:
- Not everyone uses Facebook,
- The stipulations on the auction may exclude buyers, e.g. payment only by PayPal (and I won't use PayPal),
- If the auction ends at a time when I'm not online then I can't participate.
To get the best price for an online auction there needs to be an application like eBay or GunBroker behind it to draw in the greatest number of bidders, something where buyers can set a maximum bid so they don't have to be online to win the auction, where multiple payment methods are accepted, etc.