Instead of doing math homework, I've been searching around for alternatives to Neopets with marginal success. I've always had a hunch there was something wrong with Neopets, but finally tried it out yesterday. After visiting McDonald's restaurant, I had had enough. More on the problem very eloquently described at Eileen Kramer's Neopian Samizdat. But before forging out on my own and dedicating my life to solving the problem for all time until the last star coughs out, I was poking around for other people trying to do the same thing, with mixed results.
Any other places, please let me know of them and I'll put 'em here.
One problem that seems endemic to all of these, and indeed any marketplace based system, is that people are monopolizing, quite literally. Every time one of the factory stores restocks, you may have a few seconds to select your product, but after that the store is sold out. Then the people who buy every item in this store can sell it (to you) for a greatly inflated price, and there's not much you can do but try to click faster than them. Multiply this strategy by 500,000 users, and we have a problem here.
Far from discouraged, this leads me to wonder how to fix the problem of monopolizing, in a game setting or in the real world. It's important that everyone have equal access to the market, and nobody can interfere with anyone else. That sounds like statistical independance to me. A quick fix would be to limit the rate at which you could clean out a store, or perhaps penalize players who accrue a lot of goods they don't use from one store. Otherwise you end up with the monopoly problem, due to race conditions.
A queue is good to avoid race conditions. Just have it so that someone can't take two turns if there's anyone else who hasn't taken one waiting. The CGI would have to just sleep and leave their connection hanging after a queue message. Would also have to give each person time to shop, and guarantee that whatever they see for purchase can't be snatched out while they decide. And of course if that means too long waiting periods, we can always increase the rate at which the store produces stuff, since everyone benefits equally from that!