With the potential for a small financial loss on your end, litigation would certainly not be worth the hassle and expense.

With this said, I do consider the situation. 

I purchased sub2 a handful of times for fix-and-flip types of situations, where I was in and out of the deal in 3 months.  

It will also be dependent on the previous year's financials as well.

you can always call or email the tenant in regards to this matter. i personally smoke as well and just would want my tenants happy and not feeling accused as its a big problem with a lot of tenant v landlord situations around the country. you can always say you got a report of the odor of weed and was just verifying the smell with both tenants on the property. you can restate your conditions with smoking. you can always ask if they are legally able to do so as well (meaning medical card). depending on how you want to handle it, if you want to make it a legal warning to the tenant as well, you should write a written letter sent by mail stating you got a report of weed and this is a written warning in case this a problem down the road, you have evidence to show the court if it gets to that matter that this is not your first occurrence. best of luck!

If you have not yet, try building your financial model with this in mind.  

We do about 20-25/yr so financially it makes sense.

A good real estate accountant can save you thousands of dollars by leveraging entity selection and formation, tax deductions, cost segregations, bonus depreciation and tax planning.I recommend finding an accountant who specializes in real estate taxation, business taxation, financial planning and tax planning.You may want to consider working with your accountant remotely to expand your options.I would also recommend looking for a accountant willing to work with you throughout the year.

It’s such a big leap of trust, and unfortunately, there are agents who don’t always live up to what you need in this process.An out-of-state investment can be daunting, and it’s so important to have someone in your corner who truly understands your financial goals and is committed to building a relationship beyond just getting to the closing table.

It sounds like you know how to avoid this in the future, so what to do with the situation at hand?