Just remember that Staff can control TC, but they can't control USD via PayPal. So always ask for TC to be sent before you send USD. If someone refuses to pay USD after the TC is sent, then staff can forcibly transfer that TC back (Unless they dispose of it through various methods, that staff deems as "too much trouble"). If you send USD first, and they refuse to send TC, then staff can't really do anything after they scatter your TC, they can't force them to send your USD back, all they can do is hope the TC hasn't been scattered yet.

I would suggest that while you're doing USD for TC deals, it would be smart to make sure that a staff member is online and currently active, preferably in IRC. That way you can quickly contact them in the case of something going wrong.