What makes you think that a civilization advanced enough to travel between the stars would be interested in trade? They've basically access to vast resources just within their own solar system, not to mention others.

I doubt we could really understand each other. Most first contact/ET situations in fiction tend to be between humans and almost-humans (ie, beings that may look a bit different, but ultimately think like humans and/or have similar mindsets and motivations). I think this thread is predicated on a similar assumption.