Renters paying under fair market

[Christopher R.]

I am currently trying to buy a duplex with one side owner occupied.  I am running into many properties that have long term tenants who are not paying fair market rent.  In fact, they are paying usually 200-300.00 a month under.  The good news is that most of these tenants are in month to month leases.  I was wondering if anyone could give some advice regarding buying a rental property and having to inform the tenant that the rent is going up or that they have a 30 day notice that their lease is ending.  What is the best option for this?  What are the tenant's legal rights?  When should you notify them?  Thank you so much for any information you could provide.