For, example, bear gall bladders are a huge item in the illicit wildlife trade.  The gall bladders and, for that matter, bear paws (a delicacy in some cultures) and claws (ornamental and medicinal uses) are sought after, bought and sold, to the detriment of the population of bears.

And, I'm not even talking about endangered species, here.  The trade in them (like, say, some species of parrots) is even more lucrative.

Short version - buying and selling any wildlife, alive or dead, without the requisite permits from the feds and relevant state governments, is likely (i.e., almost certainly) illegal.  

Killing game for sale - either in traditional medicine or for the table - is called "market hunting".  That's been outlawed for over 100 years.  The game one can buy in markets or restaurants is farm-raised.

Killing non-game animals and birds for any purpose - also illegal.  Under state laws, it's  a violation of the respective game codes.  Under federal laws, there's a lot of law on the topic, particularly as to migratory (i.e., crossing state or national boundaries) game and birds.  

Selling that which is legally or illegally killed just compounds the offense.

I suspect these pardonees were dealing in large quantities, were selling obviously-recently killed specimens, and/or were selling other stuff they shouldn't have been.  What they ultimately were convicted of - may have been much less than they originally did.