I bought a Intel CPU in a Forum, but was miss sold Want a refund, how law can help me?

I recently bought an Intel CUP in a Forum when I asked the seller if the Model was D0 steeping he response affirmative (I paid by cheque) but when I receive was a different version, I asked for a refund but he asked me to return it first at my expenses before he can give me a refund, I don't trust this person anymore, what can I do? how the law can help me this time? thanks