In my opinion, I think that any item bought with crowns should be able to be sold back for crowns. I can understand that the resell value would be a lot less than the purchase price, but you should be able to get crowns back for those items you can no longer use that you purchased with crowns, instead of selling them for a small portion of gold. I think this would increase a lot of activity in the game, because as rare as it might be, even the item won in battles that are Crowns Only can be sold and help everyone buy that one item they have been trying to get for ages or something they really want.
