Can I use open-source files in my item for sale?

If the author(s) have given express written permission in their documentation that their open-source files are allowed to be used for resale, then you can use them in your item. However, you will need to credit the author(s) in your file description.

It needs to be transparent to reviewers and buyers where your open-source elements come from. Whatever you do with an open-source file must follow their terms of use.