"I'll send you more than you asked and you'll send me the change" is an old scam, and likely an attempt to cash out hacked/carded funds.
You haven't really posted any "proof", just a tiny snippet of what looks like a Skype dialog but with no links to you or rikugou.
Post the full Skype conversation, links between Skype IDs and Bitcointalk IDs, any Bitcointalk PMs, TX IDs, and proof of sending $500 from a PayPal account that you own (or your "friend" owns).
Edit: and proof that you refunded the $160 in BTC of course.