eBay filed a patent that gives detailed clues into how it ranks search results. One criteria it uses: the projected demand for the item in a listing. Another: the "quality" of the seller.
The patent describes ways that eBay could (and likely does) use a variety of factors beyond mere relevance in its Best Match search rankings, which is the default order in search. For each type of criterion, eBay may create a component score, which are then used to derive the overall ranking score.
- Relevance score, representing a measure of the relevance of an item listing with respect to search terms provided in the search request;
- Listing quality score, representing a measure of the likelihood that an item listing will result in a transaction based at least in part on historical data associated with similar item listings;
- Business rules score, representing a promotion or demotion factor determined based on the evaluation of one or more business rules.
When determining a listing quality score, for example, eBay may factor in such criteria as price, condition of the item, shipping method and cost, duration or length of time the item listing has been active, a seller's prior conversion rate for all items or items in a particular category, and a seller's rating (e.g., based on feedback provided by buyers).
Some excerpts plucked from the patent filing provide further insight into factors eBay considers important when ranking search results:
Relevance score may be based on an analysis of an item listing's title (e.g., title relevance) as well as an item listing's item description, and historical data indicating how users have previously interacted with item listings having similar item attributes when those item listings were previously presented in a search results page.
Many item attributes may be considered in various embodiments, in some embodiments the price of the item and the shipping cost are the primary predictors of quality.
For instance, if a particular item listing is offering for sale a television set at a particular price (e.g., $100), the particular price may be compared with the prices of similar television sets that have previously been sold. If, for example, the price of the television set is lower than the mean, mode, or median price (e.g., $200) of similar television sets, which have sold recently, then the listing quality score should reflect the "good" price of the television set offered via the item listing.
For example, it may be desirable to promote or demote item listings that have certain item attributes or seller attributes. If, for example, an item listing has free shipping, the listing may be promoted. Similarly, if a seller has a low seller quality score (based in part on feedback from buyers), an item listing of the seller may be demoted to reflect the poor seller quality score.
In some cases, when the business rules are transparent and therefore known to both the sellers and buyers, promotions and demotions might be used to encourage certain behavior.
As indicated under the description of Business Rules, eBay has wielded carrots and sticks to encourage sellers to offer free shipping. It's worth nothing that lately eBay has been doing likewise to encourage sellers to offer generous returns policies.
The patent indicates eBay takes into account product categories when determining the importance of various criteria when ranking listings in search. For example, it stated that "with some types of items, such as antiques and/or jewelry, the seller trust factor may be more important, as there may be more fraud prevalent in the trade of such items."
The eBay patent also describes a scenario in which its demand metric takes into account transactions (sales), views, search impressions, and watch lists. For auctions and single-quantity fixed price listings, the demand metric may be based on the number of views, the number of bids (for an auction), or the number of watch lists associated with the item listing. Or, it may be based on the performance of similar listings.
You'll notice under Business Rules eBay references "seller quality score." While there is no mention of it, eBay could conceivably give its diamond powersellers, large brands, and big-box stores a higher quality score if it wished, boosting their listings in search.
Note that currently eBay references buyer feedback as contributing to the seller quality score - and some may like the concept of demoting "bad" sellers.
Let us know if any of the criteria or practices come as a surprise, and what you like and dislike about the methods of ranking search results.