Do you think your repair estimates were off on the deals you couldn’t sell?

For example;https://www.georgiamls.com/424-powers-ferry-rd-se-marietta-ga-30067/87490783 beds, 2 bath all brick ranch, 1400 sq ft built in 1953Interior was dated, had extensive damage and because it was built in the 1950s, I estimated it would need extensive rehab including plumbing and electrical replacement.

I am currently reading the book on Estimating Rehab costs by J.Scott and would like to pair it up with an actual project.

I would do my own research and find 1 or 2 good vendors, speak to them, and then let them provide the estimate.

Moving forward, the lender sent an estimated closing cost.

He's estimated to need $150K down and asked a potential investor (me) to come up with (33% or $50K) but is only willing to give up 25% equity in ownership since he is doing all of the work for the development and is only looking for a passive investor.

I have been using $3500 for my current estimates. 

Tenant claims car was damaged got estimate stating 4800 in damage.  

Many in my area are really beat up, how do I go about finding out the estimated costs for budgeting purposes to see if it's a deal or what I can offer for it?

I was planning on using the funds from the HML to renovate.I see what you mean about the slim margin, but I greatly exaggerated the numbers in my renovation estimates, to try to make sure to be conservative.