brocktowler scamming proof

I agreed with brocktowler to buy cs:go for 30 bux...the first agreement was to send as gift 15 USD before and 15 USD after the trade. He came up with some bullshit later on as you can see in the screen shot images of the conversations to where he needed it all before he could give me the game, and once I gave him all he found another reason not to accept it. I asked him to refund me the money and he stops responding. Then I threaten to dispute and he tries to call me a scammer.
http://imageshack.us/photo/my-images/94/proofmsn.png/

http://imageshack.us/photo/my-images/819/steamproof.png/

Did not know you can dispute gifts, however I am not sure how the "investigation' will turn out, looks unlikely to me.

 

Brocktowler is banned.