Either the package itself has issues I have not figured out how to fix or the model is old and outdated. Some models may get updated unity packages while others do not.

Yes! If your purchase is 35$+ you can receive a free upload including any edits added, however it has to be specifically from deergraves. Other uploads may request payment for their uploads.

If an issue is found with an asset/edit that cannot be fixed then you will sadly be rejected. Same goes for assets that require the user handling them to own them/purchase them.

Ripped assets will result in an immediately ban from purchasing any further models as well as entering any spaces run by deergraves.

The only solutions known by me is that blender is not a default app on your computer, I use blend files and not FBX.

An easy way to do this is download blender off of steam. At the top left click edit and go to preferences. go down to systems and click the register button under operating system settings, ensure you check "all users" on the little box.

Yes, you are responsible for setting up the package and model properly. You are allowed to request help from either staff in the server or someone who also owns the product.

No, unless the product has a commercial rights option you are not allowed to do so under any circumstances. Ensure you read the TOS carefully.