I'm no expert, but I think you have entered into a contract with the seller which you shouldn't break. What you can do is seek reassurance from the seller that they ARE genuine GHDs. If he/she can give you that (presumably by e mail) then you have in writing what you need. If they turn out to be non genuine you have the proof you need to demonstrate that they were not 'as advertised'. If the seller WON'T confirm they are genuine then you can reasonably ask to cancel your order since they have not been honest with you and the goods are not 'as described'. You could mention Trading Standards if you feel you need to apply pressure!
Richard
January 2009