Abstract: There may be large numbers of content items available at current content provider systems. Subsets of these content items may be eligible to participate in events, such as sales. A content provider system may determine content item eligibility for events using content item data and proactively query vendor systems for participation in such events. The content provider system may iteratively query vendor systems based on an ordered set of eligible content items. The content provider system may monitor content items for updated content items data and proactively query a vendor system if a content item becomes eligible for an event based on updated content item data. Content items associated with a sale may be sorted and presented to a user based on user and/or content item data.