They can offer triple opt-in (three confirmation emails before address is send to and also your you're billed for it, now that's quality!).
Ideally, the freer it's the better " We all like freebies, don't we? https://Blog.lenodal.com/exit.php?url=aHR0cDovL0t0dHJvbi1Wb2xnYS5ydS9iaXRyaXgvcmVkaXJlY3QucGhwP2dvdG89aHR0cHM6Ly9MYXVuY2hoYXBweS5jby9ndWlkZXMvZG9taW5hdGUtdGhlLW1hcmtldC1oYXJuZXNzaW5nLXRoZS1wb3RlbnRpYWwtb2Ytc3F1YXJlc3BhY2UtdGVzdC1wcm9kdWN0cw&entry_id=113