I don’t think I’ve ever built a WooCommerce site where the client didn’t ask: “How do I pick which related products to display.” The answer has always been “You don’t; the system randomly picks products from the same category.” No client has ever been happy with that answer.
Now I’m happy to say I’ll never have to give that answer again, and neither will you! My latest plugin, Custom Related Products for WooCommerce, replaces the default related products functionality in WooCommerce. With the plugin activated, edit any product and click the “Linked Products” tab. In addition to Cross-sells and Upsells, you’ll now have a Related Products box. As long as you’re using a default related products implementation, the plugin will work automatically to show the products you selected in the Related Products list at the bottom of the detail view, no theme updates required.
You can download Custom Related Products for WooCommerce from WordPress.org or install it from the Add New Plugins page in your admin starting today. If you have suggestions for changes, you can fork the plugin and submit pull requests with GitHub.