Worthpoint is not a sales site.
They offer a subscription service to their aggregation of sales of many types of collectibles. As such, they provide a service similar to what Stamp Auction Network is now offering with their subscription to "prices realized".
They gather their data from
ebay, many philatelic auctions, and other "estate" style and collectibles auctions.
As to the value of their data, I have no information as I have never had a subscription.
Mike