Honestly I think the majority of players are not going to get to rank 50 in more than 1 or 2 crafting classes. Even if they do most players by that time will already be max rank in their respective combat classes and have all of the equips they would need anyways. By the time a player was rank 50 in all crafting classes they wont need to buy anything from other players, at least until they raise the level cap and more recipes are released for rank 51+.