How easy would it be to trade with aliens?

Space aliens, that is:

Hickman believes that interplanetary trade could be one of the primary economic drivers for space exploration in the future. The potential problems are by no means minor, however. First of all, the vast distances between solar systems would probably prohibit the transportation of tangible goods. (Though, as Hickman points out, transatlantic trade probably seemed just as fanciful to traders in renaissance Europe.) There may however be potential for trade in non-tangible goods such digital entertainment, or scientific information with newly discovered alien species. But even this is not without dilemmas that would give Austan Goolsbee a migraine.

How will we enforce contracts or copyrights laws on a civiliation 20 light-years away? How will we set up a banking system or transferable currency without any tangible goods to trade? How will we protect ourselves from strange new ideas and ideologies that may destroy the fabric of our society? Worst of all, how will we trade with a species that may not even have a concept of trade?

It’s funny, but that last question is the least of my worries.  And reciprocal, tit-for-tat exchange would work just fine, provided that a) relativity did not slow down the exchange of information too much, and b) not too many Ohio voters watched that movie where the aliens send us their genetic information, embedded in an apparently innocuous transmission, and trick us into downloading those instructions and then cloning them en masse… 

In other words, we probably cannot trade with aliens.  Here is the full post.