Use the knowledge option in the game and search for the item you want to buy.
When looking at that item you see the option BUY from.
A list of shops will show up.
When you see the shop that you found on the BUTT site then click on that shop once so it starts tracking that shop.
That way you can see how far away that shop it and the tracking system will guide you to that shop.
Get close to the selling plinth and the tracking for that item stops.
Edit: You have to be on the planet though for this to work @Rolco
wait, BUTT saying where shop is located, giving you planet location, usually going to that planet thru TNT megahub you can find portal to that shop, most of them got even portals at shop rings at tnt megahub, having planet name just warp there, find item at knowledge tab and follow compas marker
There were like 5 shops I could not find via the portals at TnT. And the one I did find was inactive lol.
So I went to their planets, however once there I didn’t know the store locations.
Keep in mind though that the ingame information is real time. So buying everything from a selling plinth will result in that plinth instantly not showing up anymore with the knowledge option.
The BUTT website is not realtime and can (read: it will) be behind on changes.