Month to Month Long term Tenant( 9yrs)

[Gino Exantus]

Hey guys, so I’m considering purchasing my first duplex in Florida. When I went to visit the property I was I noticed that one of the units is currently being occupied by a tenant that has been living there for 9years on a month to month basis. I also noticed that the tenant is paying way below the average rent rate. The other unit that is not occupied was recently repaired and updated but nothing was done to the occupied unit .

I’m kindly asking for any advice on what I should look out for? If I were to increase the rent, what possible problems could arise? If I do not intend to keep the tenant who has been living there for 9yrs, what problems could I expect?