Duplex opportunity but I need help negotiating

I am touring a duplex tomorrow that is IMO a great investment opportunity. I have crunched the numbers using the 4 square method on BP YouTube channel. Everything adds up but there's a catch, I calculated my purchase price and rental rates not the asking price and current tenant lease rates. Here are the numbers:

Asking Price $169,000; Market time: 156 days, offers: 15 plus (all below 150K), Current lease: Duplex 1- $580 (till July 2023), Side 2- $630 (till Sept 2023)- the current owner has rarely increased rent because she feels bad asking more from her current tenants of 5 years and 14 years; No HOA

I am going to offer 150k and eventually up the rent to side 1- $830, side 2- $680. 

Where I need help is negotiating with the selling agent on getting the price down to $150k. I have spoken with him over the phone several times and he admits this duplex has been a pain to sell because the owner is listing it so high. I agree with him, it is way to high of an asking price. What can I offer in the deal that wont break my bank or ruin the deal? How can I appeal to the seller that people aren't going to pay that much for this duplex? 

Thanks in advance for all the advice!