I bought a dress for DD (age 6) from eBay and postage was given as £4.60. It's arrived, packaged in brown paper and sellotape, and the postage cost only £1.19.
The itself dress wasn't that expensive (£8.39 - although it was Mini Boden so I feel it was a good price!).
I don't mind sellers adding a little bit more for the cost of packaging materials, and the cost of getting to the Post Office, but £4.60 just sounds a bit much! But is it worth the argument...?