In stores that sell a lot of different items, it appears to be challenging for the "Related Products" under the Product Details page to accurately detect and show items that are similar to the product being viewed.

However, if store admins were allowed to select from a collection of similar products, or give the filter some sort of sample, or even select products manually, this would be a non-issue.

TLDR; Allow store admins to select what products are related to each other please.