How to narrow down the search to products from certain categories?

To make FiboSearch look for products in certain categories only, go to WooCommerce → FiboSearch → Search config (tab). At the bottom of the config page, you’ll see the “Exclude/include products” section:

Set the “Filtering mode” to “Include” and then set “Filters” to the categories you want to include in search. You can also narrow down the search results to products with given tags.

Save your changes and rebuild the index. From now on, FiboSearch will only search for products in selected categories.