Third party files may in ProcessWire may specify their own license.
3rd party files are PHP modules, templates, JS/CSS files, or any other files located in the /site/ directory of a ProcessWire installation. These are independent of the ProcessWire core (which is located in /wire/).
ProcessWire is a system specifically designed for executing 3rd party templates and modules in the /site/ directory structure. Original code in templates and modules executed by ProcessWire, and within the /site/ directory structure, are not required to use the same licenses as the ProcessWire core. Template and module developers creating original works may choose their own license.
3rd party modules typically specify what license they use within the module file or in a separate LICENSE.txt or LICENSE.md file.
Unless an alternate license for templates or modules specifies a warranty, there is no warranty regardless of license or fees.