Authorization problem.

I was selling an IG Acc on ebay, because I couldn't think about a better place to sell. It was bought 2 times (I put it back in after it failed the first time), but both times I had to send the payment Infos after I sold it and without getting the money directly. In both cases, I recieved a message later, that the buyer bought the Acc without the Authorization of the ebay account owner?? What is this? Is it because youre not allowed to sell accs on ebay (germany) anymore, or did I do something wrong? Didnt the customer actually bought it? Did ebay disabled him to pay?