Most in-game currency purchases may be refunded by selling the item back to any vendor within two hours

AH is not showing the actual lvl requirement for some items.

Information about Timewalking event quest reward item levels

What to do if your in-game mail was accidentally sent to the wrong character

What to do when you purchase the wrong item using Tokens of merit

What to do if you crafted the wrong legendary at the Runecarver, or you added the wrong enhancement to it

What may be wrong if a redemption code received with a physical Steelseries purchase is not working

Information about choosing the wrong quest reward

Information on Great Vault rewards from Delves.

How to resolve a mistake choosing the server, faction, race, name, or appearance of a boosted character