Ban the user first, then delete the comment. Do not just hide it.
Hiding a comment only hides it from most people, but the person who wrote it and their friends can still see it sitting under your ad. That does nothing for you. Banning the user stops them from commenting again, and deleting the comment removes it for everyone. There is no negative effect to deleting, so do not be precious about it.
Negative or skeptical comments under a cold-traffic ad do real damage because new prospects read them before they ever reach your page. Clean them out. Ban, then delete.