Sold WOTLK Beta key and got banned...

This is my second account. I was on Tichondrius yesterday selling WOTLK beta keys for 2,000 gold. I had 4 beta keys sent to me and i was low on money so i decided to sell 2 of them. I met a mage who agreed to trade 2,000 gold for the beta key. I forwarded the beta key invite to him to his email account. I give him the website, over vent, to register his beta key. It worked and soon he was downloading the client. Cool a satisfied customer, i thought. Later in the day i was doing arena with a buddy of mine. I get a whisper saying that he wanted 1500 gold back because the key wasn't worth it. He stated that WOTLK was coming out in 2 weeks, i reassure him that it wont come out for a couple of months. He insisted that i give him his gold back , i don't and he left me alone. I get a whisper from his friend saying that i scammed him. How did i scam him? He gave me 2000 gold for an unused legit Wotlk beta key and now he wants 1500 back because its not worth it? I got this in my email.

so he got the wotlk beta key, 2000g. i get a 72 hour ban and my key stolen. what now?

==============================================================================
Realm: Tichondrius
Character Name: Feardotlol

Account Action: 72 Hour Suspension

Be aware that additional inappropriate actions may result in further disciplinary action, leading up to or including account closure.

Offense:
Scamming another Player
This category includes:
Acquiring items or any other “possessions” from another player through misinformation, confusion, or fraud (Scamming)

Details: Character above had made a trade agreement with another character and did not honor the terms of the agreement.
=============================================================================
=============================================================================
Realm: Tichondrius
Character Name: Feardotlol
Money Removed: 2000g 00s 00c

We recently received a report from another player that they had been scammed. During the course of our investigation, we discovered that one of your characters had received item(s) or money that had been obtained in the scam. Unfortunately, the item(s) and/or money have been removed to reimburse the owner.

Our current policies regarding scammed items or money apply to players who knowingly or unknowingly receive money or items from a scammed player. If the character was found to have assisted with perpetuating the scam, they may receive an account penalty up to and including account closure. We sincerely apologize for any inconvenience you may have been caused.
=============================================================================