the idea of the museum is that the works of art don't exist physically, instead they are imagined by the artist. So when you purchase the "work of art" you get a "card" to hang on an empty wall and you "describe it to your audience."
Amazingly, the museum just made one big sale. A woman paid $10,000 for a piece title "Fresh Air," which Paste Magazine describes as:
A unique piece, only this one is for sale. The air you are purchasing is like buying an endless tank of oxygen. No matter where you are, you always have the ability to take a breath of the most delicious, clean-smelling air that the earth can produce. Every breath you take gives you endless peace and health. This artwork is something to carry with you if you own it. Because wherever you are, you can imagine yourself getting the most beautiful taste of air that is from the mountain tops or fields or from the ocean side; it is an endless supply. LINK