13. A computer-implemented method for providing a legitimacy rating of a content source, comprising: receiving at a computer system a request for a document; providing, by the computer system, an electronic document by a document provider based on the request, wherein the electronic document is associated with a content source; and providing, by the computer system, a legitimacy rating of the content source, wherein the legitimacy rating comprises a history rating and a transaction volume rating wherein the transaction volume rating is based on the number of documents associated with the content source that have been provided by the document provider and wherein at least one of the history rating and the transaction volume rating comprises a metric that is normalized based on at least one of history ratings and transaction volume ratings of a subset of content sources who provide documents to the document provider, wherein the subset of content sources are selected based on a similarity to the content source.
13. A computer-implemented method for providing a legitimacy rating of a content source, comprising: receiving at a computer system a request for a document; providing, by the computer system, an electronic document by a document provider based on the request, wherein the electronic document is associated with a content source; and providing, by the computer system, a legitimacy rating of the content source, wherein the legitimacy rating comprises a history rating and a transaction volume rating wherein the transaction volume rating is based on the number of documents associated with the content source that have been provided by the document provider and wherein at least one of the history rating and the transaction volume rating comprises a metric that is normalized based on at least one of history ratings and transaction volume ratings of a subset of content sources who provide documents to the document provider, wherein the subset of content sources are selected based on a similarity to the content source. 15. The method of claim 13 , wherein the request comprises a request for a document associated with a concept, and wherein the electronic document is selected based on a relevance to the concept.