As you've stated, it's difficult to prove your tenants are the source of the weed smell.

The measure the size of each bedroom and determine the maximum number of warm bodies that can sleep in them.

What would be interesting, is if you placed in the body of your Airbnb description texts something like:  "Please be aware that Airbnb assesses a 15.5% service charge on all reservations, which is then included in your total price."

If that will pass the smell test.As you mention use leverage.The next comments and your actions depend on your view of the future.1.  

The property will somehow smell of smoke! 

Marriot Convoy lobbies not only always smell great - they have a proprietary scent. 

You could produce an exact clone of an IC site by hand-writing the HTML in Notepad if you wanted (very bad idea).What matters for SEO is a long list of factors that the web crawlers use to rank your page - what kind of words are used in headings (that is, what does the page appear to be "about"), what types of phrases and words does the body copy of the site use, how similar is that content to other sites, how many incoming links does the page have from other "high authority" sites, how much traffic are you already getting, how quickly does the page load, how recently was the content updated, how effectively does the site render on a mobile device, etc. etc.Nobody knows the exact formula for how search engines use those factors, and they change all the time.

Water bodies, existing or you can build8.  

The smell still can run one out of the house.

Also, it is extremely low maintenance and carpets can smell overtime if you do not regularly clean them.