I always add 4 humble harvest stands to my Stones Throw Greenhouse lot when I place it in my games. My sims get rich quick by selling their harvestables in those stands. I've had them sell fish and other things there as well and I know you can buy books from it. I don't know of anything you can't buy or sell in them but I haven't done much experimenting with them. Sims get a negative ripped off moodlet when they buy something from the HH stands. But they often get huge bonus payments when they sell something from them.
