Just sell it with a quitclaim deed or do owner financing with your buyer.

For a decent quality note with a decent yield, there are a multitude of buyers at any point in time.  

I want to get in the rental property business with the 4plex etc.Which books do you recommand for get the good basics?

Should I at least get it under contract and see how the buyers react to it?

Yes, there are savvy and enlightened buyers who would buy it.

He probably will never be available to show it to your end buyer. 

1) That’s the basic relationship, Transaction Broker, 90 plus % of the time anyway. 2) make your contract, Including inspection dates, final financing and closing dates tied to the completion of roof, a passed Final Permit Inspection. 3) The commission is not detailed in your purchase contract.  

But what is the basic formula to figure it out?

If the lender had trouble get comps they like, the seller will have the same problem with another buyer and will probably understand that it is the property not you that is there problem.

Even if you repair the foundation, you will have to disclose it to the end buyer, which can scare them away or reduce the value.