I agree with everything Kammikaze said. Solid advice.
People really do suck at responding, so I would always advise that when you initiate a trade to always post a comment in the chat. A lot of time for me, this is my indication that my trading partner has responded. Plus anything in the chat log will be better for if a dispute were to happen. Speaking of disputes, I would for sure always try to work any problems that may come up in a trade. Most people would prefer this. I know my completed trades pale in when we compare it to other, but I take my trade score serious and if I screwed something up, I will make it right.
As Kammikaze said "Another way to avoid that situation is to trade with only established traders in the beginning. Traders like myself that have been here for years aren't going to throw away our positive trade reputation to scam someone for $20 worth of cards." I agree so much. I know if a new trader starts up a trade with me, I do have them send first and I will scour their few completed trades to see who they have traded with before. If I see a lot of completed trades that have some names that I trust, I will be more willing to send to them.
So, welcome and hopefully you enjoy the site.