Guild Wars 2

I suggest a merchant for returning items you may have accidentally bought, namely ones that use currency different than gold, such as bandit crests and geodes. I’m sure many people have bought items only to find out your character, or another one of your characters, already has the item/recipe. The best place for such a merchant would likely be in Lion’s Arch, perhaps by the Event Merchant.

Just playing Devil’s Advocate here, and with no judgement on the merit of your suggestion, I suspect the response you’ll receive to this is that i) items/recipes you have are already indicated as such in their tooltips and ii) when you attempt to buy such, you’re told that you can’t use it as you already have it and you’re asked to confirm the purchase. This will probably act as a disclaimer that once you’ve made the purchase, there’s no going back.

It could be argued that such items should be at least salvageable or forgeable, but that could also open an alternative way to make gold that might be destabilising (e.g. buy with badges, reforge into something sellable).

An interesting idea though..