The order in which products are shown while viewing a category is affected by a number of factors. Below are listed the influencers of product order from most to least influential.
To see how products are arranged on Category and other non-Search pages, check out How Products are Arranged on Search Result Pages.
If a shopper on your site selects a sorting option while browsing, this will act as a hard override to everything else. When a shopper selects a sort; all other sorts, boosts, pins, etc. are ignored in favor of sorting on whatever the shopper chooses.
When the top sort is selected again ("Most Popular" in this example), the page goes back to the way it was before the shopper sort was applied.
1. Pinned Products
Assuming there's no shopper sort, the top priority for showing products comes from Pinned products via our Merchandising tools. These products are shown at the top in the exact order that's been set by you in the campaign for this page.
You can see this in Search Preview by looking for the blue pin icon on products, and by looking for "Promoted" on each product while viewing in the Advanced view.
2. Product Boosting Rules
Products are then affected by Product Boosting Rules. These rules set by you in our Merchandising tools allow the dynamic re-ordering of products based on specific rules based on your product data.
You can see this in Search Preview by looking at Boosts on each product. Groupings and sub-sorts can both occur here, as illustrated by the dots and sort icons, respectively. Boosts higher in the list are more important, and a boost showing lower is always a tie-breaker for the rule above it. You can also view the boost rules and where they come from in the Sources toolbox.
3. Default Sort
The final tie-breaker when deciding how to sort products is the default sort option set up on your site, which is the top field sort set up on the Sorting page.
You can see this in Search Preview in the Sources toolbox under "Default Sort". To view the values in action, go to the Fields toolbox and show the field from your default sort. ("sales_rank" in this example)
If you have things like boosting rules set up, this usually won't make much of a change on your site. However in cases where there are no pinned products or boost rules, there will be plenty of products that could use a helpful default sort order.
This will be the only thing ordering products if you don't have anything else set up.