I'd have to say I agree with Beefy on this. As a buyer you should have considered all your options. Unfortunately, I'm guessing that you thought you wanted to save on $ but made a wrong choice in a moment of impulse/(greed too perhaps?). I'd say you can't blame the owner because you did not ask about the exchange policy. Hence, I don't see where the shopkeeper did wrong.
What's more you are trying to flame the shop in this thread. Not very nice, in my opinion. If I were you, I'd blame myself over other things. Much less to start a thread here to defame.
It's quite disturbing to have people pushing the blame on others when its your own fault.