I am a very lousy 3D content creator.  I have made some freebies, and some people have honoured me by downloading them in the first place, and I thank them for their support and encouragement. 

I say No to commercial usage of my freebies, because it would be a total embarassment to me ( and to the user) if they tried a high-quality project using my ... ahem... 3D content... koff.... It's just for fun, guys.

One can't ring-fence one's down-stream users; one can at best make one's wishes known loudly and clearly.  (edited for logic !!)

On the other hand, many commercial-use 3D items end up in the pirate zones of the internet.  Shame.  The freebies don't get pirated so blatantly, probably because it's just not "worth" bothering.  Or perhaps the pirates have some other agenda, who knows.

Eternal Hobbyist