First game I ever played was just now.

Third CPU got a heck of a Smithore production line going, was getting over 30 units of it per turn, quickly hit the spoils-down-to limit of 50, and never sold. Ever. He'd produce to above 80, then sell none of it because nobody was buying it and he wouldn't come down to the store's price- no AI would, actually.

I, of course, sold off my own Smithore holdings to keep the price depressed (it was Crystite where I was trying to make my fortune), and it worked to the degree that, despite a turn-five scare, we never ran out of MULEs, and the CPU never, ever sold any of its Smithore.

The CPU should probably be smarter about selling down to 50, even at a bad price, when it's obvious the price probably isn't going to go up- the value of spoilage has to be considered.