They'll have the same issue with the next buyer and you can always come back in a few months and make them a much lower offer once the property has fallen out of contract a few times and they are extra motivated to sell.   

But it takes time and energy from internally motivated people who take responsiblity.

I also agree that RE appreciation is unlikely to match the last dozen years, but you never know.Where I am unsure we agree is that paying $450k to improve the cash flow ~$3k (your numbers but I expect my delta wold be similar meaning both my cash flow estimates would be worse than yours but both would be worse by the same amount not affecting the difference) makes sense especially if the cost of having the extra $450k is only 6% rate which is historically simple to beat via numerous investment options and hopefully no one is investing in RE for an expected of 6%.  

Because the sheer majority of truly motivated sellers do not like agents.They RUN!

Search the BP for ADU appraisals to encounter numerous examples.

@Diana Teng there are a LOT of potential pitfalls:(So, it's vitaly important to not just find someone that you think you can trust because they tell you what you want to hear, but you find someone that their processes seem a good fit for what you want.EXAMPLE: we do BRRR Turnkeys for clients and take numerous vides we share with them - initial, worst state of any demo, when HVAC, plumbing, electrical update BEFORE walled in, before any major payouts and of course a final walk-thru video.One thing that's accurate from all the HGTV renovation/flip shows is that you should expect and plan for surprises!

Pretty much everything I have seen and read is:Find out the sellers motivation/problem and speak to solving that issue.Give an offer but explain how you got your numbers.Other than that, it seems pretty limited for negotiating information. 

The home happened to be owned by an estate and they were motivated to sell.

Let them know that you are still in the business and ask them if they or anyone they know needs anything in relation to real estate.Call for-sale-by-owners (FSBO's) Many new agents are hesitant to reach out to people that they don’t know, but these are people who are motivated sell their home.

The ones that motivate you and keep you on track.