If i may ask what exactly is a re-audit?
There's a platform called "twitteraudit", it shows how many of your followers are real and how many of them are bots. Usually it's required to check for bounty campaigns, so manager and team would know that you provide only quality traffic with your audience.
So you can do it for free just once, you need a paid subscription to do it again (re-audit), so people with this subscription usually help those who don't have it.