I've had a think about this, and the issue is game balance and ease of programming. I think it could be done if you could sell things that can be bought in the order store back to the order store for a fraction of the usual purchase price. This could be set at (say) 10%, or require some building in the citadel for a more sliding scale. Items sold would add to the inventory of the store, and hence be available for other players to purchase at the regular price. This wouldn't be a complete solution, as there are many things that can't simply be bought in the order store, so not all items would be available for a 'refund', but would go a long way to being able to reduce inventory bloat, especially if the order store was expanded a little.