Is there any regulations on buying and selling Bitcoin on eBay?
According to eBay's Stamps, Currency and Coins Policy:


  Virtual currency must be listed in the Classified Ad format in the Coins &amp; Paper Money > Virtual Currency category. These requirements apply regardless of whether the virtual currency is digitally or physically delivered. Examples of items subject to this policy include Bitcoins, Litecoins and other similar cryptocurrencies.


In particular, it appears you are currently not allowed to auction Bitcoins.