A quick tip so that I don't forget this again. By default, VestaCP will set directories to disallow listings, for example, example.com/files would show a 403 error instead of listing the contents.
Sometimes, though, it's desirable to have a list shown to the user, so all we need to do is create or modify the .htaccess file in the top level folder.
For example, in /home/user/web/example.com/public_html/files/
Add the following to ALLOW listing:
Or to DISALLOW:
Hopefully this also helps someone :)