I understand the underwriting procedure and know that even if I can provide the nominal NOI and market CAP rate the buyer needs to go through a much more detailed analysis.

I'm a former CPA, so I track every line item in exhaustive detail and had a couple of good lessons learned. 

Do I go back with additional estimates and try to get the 20k difference off our handshake agreement?

The listing states:Buyer will receive a Special Warranty Deed (SWD) or equivalent.All pictures, details or descriptions of any property, condition of title, value or otherwise is provided for informational purposes only and may not represent the true and current status of the property now or at the time of sale.Please contact the listing agent directly with questions or inquiries regarding this property.Xome Inc. companies are affiliates of the seller and/or servicer of this property, Nationstar Mortgage LLC d/b/a The title detail document has been prepared for informational purposes only.

thanks for the detailed answer joe.i think i have to add a few more details to make it more clear.- my plan is not to buy only cash going forward. working plan is in a year or two is have a credit score, get a mortgage etc' so from that point on i will not be putting 100% cash.- cash flow from the rent is my not my only income source. assume that no matter what i will be able to put money to buy a new rental at least every 2 years, taking the 12k+extra amount (whatever that my be)+loan (whatever down payment i decide to put)- regarding flipping - i don't mind the work involved in this process but as i am not living in the us, i find it hard to do flipping. at least not when starting out.  

I would be happy to discuss further if you want more detail than that.

We are currently sitting at 58 units total units owned53 additional units available to us the moment we have the financing to bring them down4 completed flips3 flips in the finishing stages3 wholesalesWe own and operate 2 AirBNB propertiesWe own a 20 lot mobile home parkWe purchased a historic limestone Inn which we will be converting into 17 apartments geared towards servicing our military clienteleI earned top producer status for my 2nd year and am opening my owner brokerageI'd like to go into detail on not only the keys to my success this year, but also highlight how extremely important my failures are to my success.

What options does an investor have when a rehabbed house will not or does not sell within the estimated time?

We are fans of cozy.co and I appreciate the issues related to cozy detailed here. 

I'm a licensed realtor so I have access to the MLS, but I haven't researched the outside of Boston in detail.