I am aware that at the "end of day" screen one is supposed to be able to buy an upgrade for their booth allowing them to use the space bar to enter inspect mode and use the tab to toggle the stamp bar, however there is no instruction stating where to look to purchase the in-game upgrades. I have searched through the "end of day" screen trying to find the upgrades with no clue where they are. if you found them, don't simply tell me that I can buy them on the "end of day" screen, as I already know that (apologies if I sound rude), but instead explain how to get them at said screen.
The booth upgrades become available in the end of day screen on set days during the game. There's nothing special you need to do to trigger it, you just need to make sure you saved enough cash to pay for it!