As it stands now there is little to no reason to sell things like gear or augments with such limited space in the player shop compared to stackable items where you can be selling many hundreds of generic items for similar profits.
An example is prisms, I can sell hundreds of them at a time for 1-2k each, while if I want to list some cool augments or pieces of gear even for the same cheap price I can only list maybe a dozen or two until my shop is completely filled. With how many pieces of gear and augments there are that can be of use to somebody who might want to search for those pieces, its very tedious to do so currently because nobody is willing to fill their shop with niche one-off items and only are sell generic stackable goods.
I know for sure the intent for these player shops WAS to sell these types of items because the market golems have an extensive search feature for gear and augments that is underutilized by the player base because no shop sells any of these things, mostly for the aforementioned reason, and not in any quantity that would make searching for gear players are selling a viable option to find cool pieces to buy and use.
A somewhat workable solution would be to scale the player shop slots with your retail management level + the types of items your selling, for example at level 10 you might get 100 slots, you would be able to post 100 non-stackable items (gear, augments, misc unique items) OR if you list a 70 stack of yew logs this would take up 2-3 slots, with some basic calculation you can equate the current static shop size limits to a new dynamic shop size limit with stacked items to not impeed existing stackable generic shops while also encouraging people to start actually selling the cool gear and mods they are getting.