Seller Financing - Above FMV w/ low int or Below FMV w/ high int?

[Sam Horton]

I am currently working on structuring a deal for a 3 unit in Boston. The current owner has 100% equity in the property. The owner loves the cash flow but does not fancy being a landlord. I want to approach the owner and inquire about seller financing. Since this would offer the owner cashflow without the headache of being a landlord. 

In my opinion, the MF is renting $200-300 under market value in this particular neighborhood. The owner verbally said they net $2800 per month, so I believe this to be the sweet spot for her cashflow. Values in this neighborhood since 2015 have gone from $215/sqft up to $295/sqft now and there is still a lot of growth to come in my opinion.

If I am looking to hold this property for a long time. Should I structure the financing with (A) below fair market value sale price with a higher interest rate or (B) go above fair market value sale price with a lower interest rate? Any tips/tricks that you might have picked up on when going through seller financing would be greatly appreciated as well.