I don't allow smokers period so I don't think I could comment.

In your country, anything over 4-5 PCi/L usually comes with a recommendation to vent the radon to the atmosphere external to the building envelope.  30 PCi/L would present a high risk factor towards developing {lung} cancer {particularly among smokers}.

Go with the gut, avoid smokers and everything probably works itself out

I for sure agree that advertising "420 friendly" would drive away families and none smokers, but isn't that the idea of having an intentional avatar and customer in mind? 

The only downside is there is a smoker next door. 

Actually this is a better post on ozone.http://www.biggerpockets.com/forums/67/topics/78889-smoker-rehab-keys-to-success-with-tobacco-smoke--before-after-pics

I would say that either qualifies him as a dealer or a big time smoker.

I've had success cleaning up after a heavy smoker who used my approach (before I acquired the property).

Accept that your units may attract other smokers and users of other addictive substances.

I put in my requirements that they must have a 640 credit score and at least $xx,xxx of income(35x monthly rent) and non-smoker, and so on.