It must be significant, latent, unseen, not obvious, uninsurable title would be a good reason, an inspection report that mentions the place is about to fall in due to wood destroying insects would be a good reason.

If the amount of taxes, assessments, interest, and penalties actually payable when the deed is transferred to the purchaser exceeds the county treasurer's estimate, the officer shall certify the amount of the excess to the treasurer, who shall enter that amount on the real and public utility property tax duplicate opposite the property; the amount of the excess shall be payable at the next succeeding date prescribed for payment of taxes in section 323.12 of the Revised Code.

Plus an appraisal and insection on a duplex is expensive.  

And I don't think you want to fall into an Interest Only trap, you will want to pay principal down.

Also, the option period in Section 23 of the standard Texas contract is a "any reason or no reason" clause. 

It seems easy to fall into the trap of looking at auctions from the North Shore of Boston all the way up route 93 North to the NH border.

A “tax deed to purchaser” that conveys title free of all encumbrances of any kind existing before the sale, with certain exceptions as stated in Section 3712 of the California Revenue and Taxation Code, is issued to the successful bidder.

I've read about painting the basement with a polymer type paint to prevent ground water from leaking in but the basement opens into the crawl space under the house and I'm afraid that any water from the crawl space will just be trapped and have no where to go we are talking about 12 to 18 inches of water.

The point is, this is a constant in this business, but you get better at sniffing out the BS and avoiding the traps, as time goes along.

I am raising their awareness that they need to consider all factors and not fall into the trap of focusing on only one thing like cash flow.Again, thanks for providing the yin to my yang, as all good discussions need to be strongly supported by both sides.