Greedy shop provides expensive and rare materials in very afforable price. Imagine a 500,000 worth of zennies in exchange of 20,000 zennies. Greedy Shop can only be found inside Toy Factory 1F and location and spawn time is random and also it varies per channel.
Go to Al De Baran at the most upper left side of the city, there you will find a santa, talk to him and he will bring you to Gingerbread City. Theres a portal there that leads to Toy Factory.
You can summon the greedy shop by clearing the Myst case with dark aura at the lower left of the map. If you can't find the myst case, then the greedy shop is around.
Changing channel will not change the items being sold in Greedy Shop. The Shop resets daily.