Easy!
Engineer-ish types take this to mean that the line is arbitrary and therefore irrelevant, concerns addressed by that distinction are invalid, and efforts to circumvent/exploit it are victories in the battle against analog logic. Other people understand that fuzzy definitions do not mean that the distinction therein is imaginary, merely difficult to identify.
If you've ever heard the phrase "don't throw out the baby with the bathwater," it applies here.
One solution might be to pass the fine onto the renters, but that leads to another problem: "Quiet" renters would probably be more put off by the possibility of an extra surprise charge than "Party" renters. The latter category probably ignore the penalty clause when booking the apartment and then try to avoid paying the fine after the fact. So now your set of renters is mostly loud partiers and the problem is even worse.
My post was in response to the parent, which suggested that any property "solely" used for short-term leases should be regulated.
I was not suggesting that was a useful or appropriate test. Leaving aside the question of whether regulation is necessary, a "dominant purpose" or even "substantial purpose" test would lead to less absurdity.
