The store is always open, just put items on the shelf
Viewing post in Just Start A Market jam comments
That it is, I managed to sell an apple. Turns out my problem is mostly technical - it took me a while to place a shelf, I clicked around until I found a spot where it finally happened. It's the same with other tools - I can remove the floor tiles (though I have to click a bit lower than the tile itself) but placing new ones, or walls or other things is very hard and random.