Items bought on gems to be sold for gems

In case I buy an item for gems why can’t I sell it for gems?

You purchase something for money in a shop, than you get bored of it and sell the item on ebay. You will get money for it, not chockolate or chips.

My proposal is to be able to get at least part of the same payment method back when you sell something.

I would love this idea even if limited to members within an alliance or in game friends. Flare would still make money and alliance members or in game friends can help each other.