I don't insist because then I have to police it and I don't want to do that.

There is no point in you trying to restrict them to a certain number or people or police a higher rent per person.

Call the Police!!

If the duplex is:1 - in a really  bad area 2 - not along the edge of the bad area3 - is not in an area designated as a redevelopment zone4 - in a neighborhood that has police trust issues associated with it.Then I wouldn't touch it.

Obviously, the police were on your side - what is there take on this?

Our rentals are in the more desirable parts of town, lower numbers  more quality tenants (UNBC students, CN rail employees, police officers, sheriffs, and so on).

Then, they can call the police and get her for harassment.  

And now you are trying to police the tenants' use of who is using the washers/dryers.And if they're in-unit, you are now paying for the water for their relatives to come over and use their washers.And if you try to charge them an additional fee if they put in their own washers, they will try to hide them. 

When you put it like that, people will either not want to get involved, or they will become major dramaholics.If a crime has been committed, tell the police and let them do the investigating.I've been screwed by a management company, as has my daughter - before my days of being a manager.  

Should he encourage the existing tenant to call the police/gather more/better evidence?