Suggestion: Maybe more interesting shops in game
Explanation: shops with more articles fx some of the items, that´s in the game
Items could be on depending on quality. Rare or good items occationally on for shorter unknown and allways changing times, while common items can be seen more often.
So that people don´t really know what´s for sale when.
Prices depend on quality and rareness of item, but can variate too, as long as items don´t get too cheap, so motivation for achieving items through gaming doesn´t get lost.