From a legal standpoint, I'd imagine copyright etc would come into play.
Then again, look at garage kits. Do the makers of these kits go through the whole process of approval, before selling/distributing their goods.
Not being a solicitor, I wouldn't know much about it-apart from what I've read.
People post/share their creations on sites like Thingiverse all the time. If copyright was such a huge issue, that site would be gone overnight.
At the end of the day,it all boils down to money.