Who do I talk to about a trade gone wrong? Is there anything I can actually do?

Go to a mod. I think Phantalien is in charge of dealing with knuckleheads now.

Talk to one of the moderators and explain your situation. I know of phantalien, quebbster, and there's some others but my memory stinks for names. lol

There are a few of us that are going through the same thing with another trader. Hasn't sent or gone through with deals for about a month now and hasn't been on since the 29th period. I've held back on the negative feedback but his pm box is full too and part of me thinks this person might not come back and straighten this out. So yeah your situation is an all too familiar one around here (although there are a world of more good traders than bad here).