Nice! I’m waiting out on KSP2 for now - still have lots to explore/try in KSP1.
I was curious about it once when I was considering “hustles”. One of the biggest issues may be finding a high-traffic location where you are allowed to operate a vending machine. But if a place could use one and will let you operate for cheap/free, you could give it a shot. One learns a lot from trying. Odds are the work & issues may make it tougher than it seems on the surface (may not be as passive as you think).
I’ve seen it too for some homes (relisting lower) - unsure if the market is falling or just flat.