Honestly?

Bots farm crystals 24/7 from under the map and stick them on the marketplace for such a low amount that it's hard to resist just buying them.

Instead of farming crystals for 12 hours, I could catch a single rainbow carp and sell it for 3 million, and buy up full sets of crystals instead.


Having said that.... I am intersted if somebody else has a more efficent idea and location.