Sorry, but according to the GHD website, the hair straightener you're selling is counterfeit. Aside from the false hologram code, there are numerous other methods of determining if it's genuine or not, and all of them are very clearly detailed at http://www.ghdsrepairs.co.uk/fakeghdguide.html

I suggest that you remove your listing immediately before ebay do so and also hit you with a policy violation, and possibly even restrict your selling privileges.