Hello,
Your similar listings block should show the listings that matches either with its category or tag, because the default logic for related listing is based on not only tag but also category as well, means any listing that matches with its category or tag will be shown to related listing block.
However, you can change this logic to show the listings that matches with both category and tag from directory settings page. To do that go to Directory listings > Directory Settings > Single Listing page and look for an option called “Based on” (bottom of the page), choose “Category and Tag” and then save changes.
