Returning faulty purchase

I have been told that I can exchange the item I have purchased which broke after half an hour of usage. I wanted to return it and get my money back but seller said she will send a new one out as she does not do refunds. The seller wants the item returning but will not reimburse my postage costs to do so. Is this normal/allowed? I agreed to pay a set amount for the item on a buy it now and a set postage amount was listed. Now the item was faulty I am expected to pay further postage costs. does anyone know how to prevent this?

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Orignal From: Returning faulty purchase