I remembered someone suggesting this before but couldn't find the thread for it, possibly because the suggestion was on discord. The idea is that extra usershop slots could be bought much like inventory slots, with the price increasing which each purchased slots (maybe 5 at a time?). As someone who is trying to mass-sell their special and potion ingredients, it would help a lot!

I love this idea! The only thing I'd propose for it is to make usershops partially collapsed (display only some items, and at the bottom is a big "Display All" or "View Full Shop" button) so that I'm not scrolling down forever on a rich player's page.