Duplex tenants way under market

[Samantha Klein]

I am interested in purchasing a duplex from an elderly couple who just remodeled the 3 bedroom unit and a new tenant moves in tomorrow at only $500 a month, market rent is $800-850 for the unit. If I bought the property, would it just be easiest to non-renew the tenant right away? They will be on M2M leases as the couple only uses M2M to rent. I don't think they'd be too happy getting their rent raised right away and I can't just lose $300 a month. What would you do?