If I download a 3D file, whatever the format, free or paid for, I'll open it in my preferred program and check it out thoroughly and in some cases modify it to suit the application. Over the years I've encountered little errors in other's drawings that needed correcting so that the final render (for large format printing as exhibition graphics) looks good. It makes sense to me that if you're going to commit a file to many hours printing time on your own (or a bureaux) 3D printer then checking the file and arranging elements to suit a better print arrangement is sensible.
There are loads of free 3D files available online for personal use, all given generously by individuals that enjoy the creation of the original model. Using someones drawing and modifying it was a good way for me to get to learn Blender in the way I needed to use it. Other than asking that a download is not sold on, there's nothing else you can object to.
Thingiverse has been very useful for improvements to my own 3D printer, all generously given by other users. Some modify the downloads and credit the originator when re-posting (again for free) so that we may all benefit from the shared experience.