On the poxnora.com marketplace, I've noticed that the avatar I own is showing as available for purchase, as well as all of the single player campaigns. I have not attempted to buy anything that I already own with gold, because I didn't want to need to request a refund if the transaction completed. If the purchase is blocked in the transaction process, then please ignore this report. If it would help your testing, I would gladly try purchasing an item I already own wiht gold.
I believe you will hit an error if you try to buy a campaign you already own "You are not eligible to purchase the product specified. If you believe this is an error, please contact technical support." I have not tested this with Avatars yet.
As a precaution I checked this out and you do get a warning when and the transaction is canceled if you try to purchase something you already own through the Marketplace.
