Can you Properly Analyze a Deal if you can't see Inside?

[Matthew John]

I'm trying to analyze a triplex that's for sale, but the units are fully rented out and the owner wants a written (and accepted) offer BEFORE scheduling a time to see inside. 

He then said, to go inside I need an "insurance inspection" or to go through a contractor because the tenants don't know it's for sale and he wants to know I'm serious. 

The triplex is listed for $149k and it's renting for $2035 with current tenants in place. 2 units have Section 8 Tenants in them. 

The reason to sell is to "alleviate some of the basic property management problems", but it's managed by a professional property management company. 

Stats about the deal

- Built in 1920

- Last renovated 12 years ago (roof, kitchens, furnace, floors, electric, and "90% of plumbing")

- No Central Air

- Garage converted to shared coin operated laundry/storage

The seller is an international investor. He would like 20% down payment Land Contract at 9% interest on a 6 year note. 

I don't like the 6 year note on 9% interest and can get better rates with a bank loan, but I would like to come up with a fair offer for him based on the necessary repairs. With the property being rehabbed 12 years ago, I know it's going to need some CapEx work done shortly.

Without being able to go inside, how do I come up with a far offer for the seller?