If I charge £5 for an paperback book then there is £2.80 postage charge, how much money will I get (less fees)?
From the £7.80 - Amazon take their fees - dependant on category - in this example BMVD = 15% + VAT
Leaving you the rest
From the rest you have to pay the postage to send the item, buy the item, package the item AND make a profit.
Use caution though as some books will cost less than £2.80 to post so you will need to lower your ITEM price to remain competitive......and others will cost more than £2.80 so you will have to raise your ITEM price to cover your costs.