Lots of Mason's ironstone was available on the auction sites, but none of it included a jug. We found no matches on the Web. In many antiques categories, there is two or three times as much price data available on the Web as there was 16 months ago. There is also a wealth of background information to be found, giving new perspectives. Cleverness and persistence are still required in using search engines or agents.
Auction sites provide some additional information when a sale actually happens.
Often, especially with better merchandise, bids never reach the seller's hidden reserve. Even when they do, you must follow the bidding for days or weeks until closing to see a hammer price. Auction sites do show what is hot. They are also sources of information on legitimate reproductions. On-line price guides for fine art have been around for several years.