It's allowed and it's more likely to be "trade-at-your-own-risk", especially with strangers. You can also trade for items from the Item Mall in exchange for Cegels. For example, you want to buy an XG Equipment from the item Mall but you don't have RPs, you may look for a player willing to buy the item for you and once he get it, then you trade as normal. The risky part is giving out codes before the Cegels were delivered.
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