Is the delivery address to a remote zone,Highlands, Islands and Northern Ireland or Channel Islands? This will have a surcharge added.
Also as you're here you need to change your account to a business account,a private account is for sellers clearing their own items you are selling multiples of new items.
It's simple enough to change here ChangeRegistrationAccountType
eBay will be reporting all sellers who sell more than 30 items a year soon to HMRC.