Thanks for your reply. The parcel arrived and the beauty products were sent in a box which had already been used.

 It came from a private seller who purchased the postage at the Post Office where £3.99 is correct.

 I thought all private sellers had to use simple delivery and EBay worked out the postage cost, so how did the seller manage to change the price? Or have I missed a message about private sellers being able to change postage costs?