How's this owner finance deal on a duplex?

[Robert L.]

Here are the details:

Duplex will be vacant when we close on property (the owner is moving out of the unit)

Rents are potentially at least $700 conservatively, or $1400/mo. once rented out

The duplex is worth between $85k to $100k (I had a hard time coming up with exact comps)
I estimate a 45% expenses (on the high end) which put me at a 11.63% CAP rate

Repairs are about $35,000 (it needs all kinds of updating, but has good bones and appeal once finished)

I offered $45,000 purchase payment with the following terms:

$25,000 down payment and $20,000 in 18 months

18 months of NO PAYMENTS

A 12% interest charged only on the balance

Balloon at the end of the 18 month period (i.e. $20k balance)

Therefore, 12% interest on the balance ($20,000) is $2,400

Total seller gets is $47,400 after 18 months.  

This gives the rehabber time to fix property up and get it rented for no payments to the seller

I plan to flip this property for an assignment fee of like $5,000

Is this a good deal?

Thanks,

Rob