Duplex Purchase with Bad Tenants in Place, Pennsylvania

I am considering an placing an offer on an occupied duplex.  I had a contractor walk through the place and am comfortable with the condition and amount of work it needs.  The biggest concern are the tenants.  The listing agent has informed me that the tenants have been a problem for the current owner.  Both units are under rented and the tenants are both month to month.  I have asked why the current owner has not raised rents or terminated the leases, but have yet to get an answer.  I was most recently told that the tenants have signed a 60 day sales termination which states they must move out within 60 days of sale if I don't want them to stay.  My question is, why would you need a 60 sales termination contract on month to month leases and what else seems fishy about this?  Thanks in advance.

Gwyeth