bath vents

Hi all,
I did an inspection today on a condo built in the 70’s. both baths had moisure stains above shower on ceiling and walls. There are fans installed and they seemed to work. I suspect that they do not use them, since the buyer (also the renter) made a comment about not ever using the shower in kids bath.
I am not sure how to write this up-should I recommend replacement of fans or simply suggest using them, monitoring and then replacement if needed? Are newer fans any better/more efficient?
I don’t want anything to come back and bite me later.

If the fans are working and are properly vented, roof is not leaking in addition, then report the obvious (use those fans!).