Referral-based sponsorship of access to content item sets

A memory device storing instructions that, when executed on a processor of a content item host, cause the processor to fulfill requests for content items of a content item set by:

• offering respective content items through a first offer associated with a sponsoring referrer that is providing sponsorship to the content item host for the content item set and, concurrently, a second offer not associated with a sponsoring referrer;
• and
• upon receiving from a requester a request for a content item:
• evaluating the request to determine whether the request comprises a referral by the sponsoring referrer responsive to the first offer;
• for requests that comprise a referral by the sponsoring referral responsive to the first offer, providing a full version of the content item to the requester;
• and
• for requests responsive to the second offer and that do not comprise a referral from a sponsoring referrer, providing a limited version of the content item to the requester.

A method of providing a content item library to a set of users on a server having a processor, the method comprising:

• executing on the processor instructions that cause the server to:
• upon receiving from a search referrer an offer to provide sponsorship to the content item library, identify the search referrer as a sponsoring referrer;
• and
• upon receiving from a user a request for a content item:
• evaluating the request to determine whether the request comprises a referral by a sponsoring referrer responsive to an offer by the sponsoring referrer to provide the content item;
• upon determining that the request was referred by a sponsoring referrer, provide a full version of the content item in response to the request;
• and
• upon determining that the request was not referred by a sponsoring referrer, provide a limited version of the content item in response to the request.