...or your neighbor could open a meth lab and you may never know about until you find out that half your building has cancer from inhaling the fumes.

We have condominium boards and neighborhood regulations in place so that if or when there is bad behavior there's recourse against those actions (yes, I know most condo boards would have regulations against renting. Most of the times they wouldn't get involved unless there was an issue though).

One of my neighbors rents out their place on Airbnb almost every other weekend. The tenants are almost always well behaved... unlike an owner that lives on my floor that I've had to have the condo board send a letter to because of late night parties.

It doesn't matter if they're a sketchy couple, and local law enforcement would provide for removing any meth lab (or other illegal activity) and the associated people.