I bought a pair of boots at auction, paid around £30 with postage being quoted as £5.50.
When the boots arrived, the packaging had the postage cost stamped on as £2.80
I emailed the seller & politely pointed out the discrepancy, asking if they would consider refunding the difference.
I got a reply, stating that she "does not give refunds, postage costs were estimated at time of selling &by entering the
bidding
Iprocess I had agreed to that; also that sellers generally over-charged on postage costs to cover packaging etc.