Suggestion for Expansion Items

For a lot of players, mountain expansion items appear too frequently in the global trade market such that other useful items used for upgrading or expanding to other areas do not appear at all. My suggestion is that once a player unlocks all mountain areas, mountain items stop appearing in the global trade market. They could still be earned in contests, shipments, etc. such that their value remains for selling, for after unlocking all areas, there is no point in buying mountain items from other players. Balancing the items available at the trade market would help improve the experience for players, so any action on this issue would be appreciated.