Is that even the same as putting it on the guild merchant? I finally broke down after months and I'm trying to use this system but I can't figure out how to assign my own price. It's giving me a really low default price .... help!
Yes, guild store is the same as guild merchant (which you can access at the actual merchant in-game, or at any bank). On PC; when in the 'Sell'-tab, if you click on an item to sell it will load some price details in a column on the left-hand side of the screen. The price in that column should be clickable, so that you can change it. I have no experience with ESO on consoles, so don't know how it would work there.. but it should definitely be possible. Maybe look up a youtube video to see how it's done?