If they are VERY professional, they will have their processes in writing as verification that policies are enforced equally and fairly by their entire staff.6.

I enforce late fees and even though I have a tenant that lose their job, they will have to go.

The city is much more aggressive about enforcing the rules than in many other countries and they are shutting down illegal Airbnbs.

Enforcement is a different issue.

We write an automatic 5% rent increase into every lease so that way it feels more incremental to the tenant and the expectation is there but we don't always enforce it so sometimes it feels like we did them a favor.

Airbnb doesn't want to be in the position of enforcing compliance of local laws for their users, but it is unavoidable.

Is the letter of non-renewable enforceable by law? 

They have hired a third party to monitor and enforce this.  

You would charge them rent (I'd recommend even having an enforceable lease in place). 

There is also wording that the dog should be leashed at all times on property, but this would be hard to enforce because we are training our pup and often times have him off leash to teach come and other skills.