Don't do this to your supposed nice guest. Either slam him or don't. You can't have it both ways. If you would really have him back, then simply write:
Mike and his wife were nice guests who even helped with some maintenance issues. Recommend.
Then leave the part about the unregistered guests in the private feedback. If he ever enquires again, be really clear about that.
If you would not have him back, write something more scathing.
Unfortuantely Mike and his wife were not a good fit. They were pushy about bringing unregistered guests even when I asked them not to. Can't recommend.
Then no one will ever rent to him again. Think about if that is really something you want for your "nice" guests.