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very simply put, if what is being offered is what is sold then it is legal. that is, if you get what you bought it is allowed. if, in buying something, you are assuming certain things or otherwise expecting something different because of the way it looks, that is not illegal.
it sounds to me that the pic of the item led you to believe something other than what it was. the information, though, did not state anything that was untrue. if so, it is legitimate. this is not a loophole in the law. it is merely a buy/sell community.
i am sorry for the situation but, as you stated, it does happen all the time and, thus, you need to be very careful on those sites.