The inspectors are not allowed to issue violations based on online advertisements.  So far DPP admin and corp counsel will only allow violations to be issued if the inspector can catch the visitors and they have to admit to the inspector that they rented for less than 30 days.  Then they can issue a violation.  A second violation has immediate fines so after the first violation the owner wises up and tells their vacation renters to either ignore the inspectors or tell them they are non-paying friends which is what my neighbor does on Nohili Street in Hawaii Kai.