A significant problem with single source sites is that they lack transparency by their very nature. This fact does not automatically imply that the site is not trustworthy. It does mean that there is no way of determining a site’s trustworthiness and operating characteristics independently. However the site operates, it operates as a monopoly. Monopolies, by their very nature, make and execute their rules unilaterally.
An excellent example is Web of Trust. Their service consists of an add-on to most web browsers. It displays a small circle that indicates whether the site you are on is trusted in one of five different categories. In theory, this is a good idea. However, the potential for abuse is unlimited. In my use of the service, I found that it indicated a poor reputation on sites that I had used for years. Upon further investigation, the service seemed to hand out bad reputation to sites along political lines. In my opinion, this practice invalidated the entire utility of their service. While purporting to represent one kind of offering, a utility for determining the site’s trustworthiness, they in fact used the perception of crowd sourced trustworthiness to push a political agenda. They then used the threat of a bad “reputation” as leverage for them to sell “badges” of trustworthiness for up to $750. Apparently, they had this in mind as a business model from the beginning.
Further research demonstrated that Web of Trust has engendered a significant amount of hostility from users and self-described victims of their service from all over the world.
I submit that all this outcome is not unique. In fact, this is the commonly expected outcome when someone operates a monopoly. It could have been avoided with true distributed, peer to peer interactions, themselves designed to create verifiable trust and trustworthiness. It is apparent that as time goes on, users of the Internet are evolving to reject monopolies, even the benevolent ones.