Maybe I'm wrong, but it looks as if someone has exported, textured and rendered some arbaro trees (straight out of the provided samples, no less) and are selling them for $20 US... see here:
Not sure if this can be construed as a violation of the licensing, but the least they could have done is credited your work...
I think you're right - the contents are listed as:
15 Trees in OBJ format
* Black Tupelo
* California Black Oak
* Desert Tree
* Fan Palm
* Fir 1
* Fir 2
* Lombardy Poplar
* Ornamental Asparagus
* Royal Fern
* Weeping Willow
If anyone's interested these are being distributed by Vic Haynes graphics http://www.vichaynes.com/
Even if this isn't a violation of the licence, it's a big rip off in my opinion - I hope nobody's bought into it. It's like selling blank word documents.
Since the software is under the GPL and since the tree files are part of the software, I would think the GPL license also applies to the original tree files.
However, the person is selling the OBJ files, something exported by the software and not part of the original software. Therefore I would think this is not a violation of the license. However, it speaks clearly against that person's work ethics - or that person must be pretty desparate or uncreative… ;)
Erlend S. Heggen
According to GNU.org's take on GPL output, he seems entirely within his right to do this. It's still highly unethical, and no one would be well served by buying these assets.