I am going to move this thread from the FileMaker Community Feedback Space, which is specifically for input on the Community itself, to the Discussions Space where you should receive more views and potentially more advice on this topic!
I believe this is what you are trying to do. I would caution you to at least lock down the text values so that they cannot be editied. Typos break relationships. A better way to do it is to have a subcategory table that gives you all of your category and sub category ids and then add that sub category to the product and go through that relationship. That would allow you to have all IDs instead of text values for your relationships (always better)
With your file's current structure the following file does what you want, I believe.
Thank you for the help. Since my Org post I kind of came up with the same idea when i was reading a post on here with kind of the same conditional v_list set up. Ill take a look at the file and see how you set it up. Thank you again. Filemaker rocks!
You might also find this demo file helpful. It shows several different working examples (each designed differently) of Hierarchical Conditional Value Lists (Where Conditional Value List A, limits the values for Value List B). You may find some additional ideas here that you can also incorporate into your solution: