That's interesting that they need someone to complain?
Vancouver just enacted a similar law to Boston's - AirBnbs only allowed in a secondary suite in a primary residence. In exchange for being allowed to continue operating in the city, AirBnb requires a city business license (which is only granted for secondary suites) from all Vancouver BnBs, and forwards the list of all BnBs to the city every month. Then if an address doesn't match up with a business license, the city fines the property owner. If you don't pay, the city takes you or your house to court and you get a nice fat lien on the property.
This doesn't seem to work as well with condos and apartments, though. I think the city has left enforcement up to strata orgs which is probably a mistake?