Regarding your CoC and returns, that's personal preference.

I am wondering what are some resources, preferably free, to get market data for the area I work in?

While you're at it, retain records of all your interactions with her.

Call me crazy, but I prefer to spend my money on people who will actually see the inside of my houses, not a scheduler

My home is paid for and I need to downsize but prefer to purchase new home before I sell this one so I have somewhere to live.

So I only have four options- go through with it at $18,000, find an investor with experience that wants it for rental, Negotiate with a price to backout of a contract to pay the seller for lost of time and opportunities, or wait until he sues me (which I prefer not to get sue by any means- as the result to be ending results -based on the contract terminology would mean I would still have to buy it, and then I would end up paying some lawyer fees as well). 

However, some sellers and their Realtors will prefer to work with a local lender.

I’m doing due diligence on a triplex and duplex that owner prefers to sell together!

Would prefer to buy and hold but may be better as a flip. 

Have the licensed plumber that was initially called for this issue provide you with a report of the items found as the cause of the blockage and the recommendations, preferably you should also have photos of the items causing the blockage.