Poor quality item and not recieved refund

[290453silu]

I purchased an item and upon receiving it I discovered the quality of the item was not what i was expecting/not accptable as far as I am concerned. The seller in their listing had asked a buyer to contact them prior to leaving anything other than positiive feedback so I contacted them and described the issue I had the the item I'd purchased. They responded saying "fair enough" and said I would receive a refund (Paypal) by that eve?ing. That was over a fortnight ago. I contacted them again to say I had not received a refund and have heard nothing back since. What is my next move? The item is not that expensive (£17 odds) but quite a bit of that cost will be postage.I don't see why I should have to pay postage to return the item which is substandard.