This sounds like a heck of a lot of work, surprised anyone would spend the time:
Violators often avoid detection by deleting their postings during the day when enforcement staff is in the office and then replacing them late at night or in the early morning hours when potential tourists are awake and booking vacations.
The study says that only 187 of the 950 short-term rentals in Santa Monica between June 2015 and October 2017 were licensed with the city according to its 2015 Home-Sharing Ordinance Rules.
Why would cities create rules that would result in so many "outlaws"? Sounds like they made a mistake.