Why was I charged a postal fee as a seller

[stegard63]

As a first time seller, I was charged £2.69 to send the parcel whereas the buyer was only charged £0.87. What did I do wrong? Thanks 

[tobiasd4]

Buyers only pay postage option you list.

You can't send a book for 87p.

You have to check weight and size of packed item before listing.