After 2 weeks and 30 showings we sold and made a very small profit.

Most of the duplex to quad you see that meet this rent to cost ratio have one or more items that disqualify it from it being something I would purchase.However, seeing the land is already owned and it is to be better leveraged it seems to be fairly easy to achieve far better than a 0.75% rent to cost ratio on rented ADU buildings. 

Zillow, Trulia and such gives some information but frequently its not sufficient (ie Too few comparable home sold within the 0.5 mile radius or even the same zip code). 

Check sold comps in the immediate area. 

Code Section 40-10-74 says: If the mortgage or other instrument creating a lien under which a party seeks to redeem is duly recorded at the time of said tax sale, the said party shall, in addition to the time in this title specified, have the right to redeem said real estate sold, or any portion thereof covered by his mortgage or lien, at any time within one year from the date of written notice from the purchaser of his purchase of said lands at tax sale, served upon such party, and notice served upon either the original mortgagees or lienholders or their transferee of record, or their heirs, personal representatives or assigns shall be sufficient notice.

Sold in year 5 for $104.5k.Duplex, $83k + $3k rehab.  100% finance, don't remember payment. 

Did you see the new item that passed in Saint Louis Park?  

[Note: Any local Realtor should be able to give you the (sold comps) ballpark value].

Additionally we have in the contract that due diligence WILL NOT start until ALL items are received  listed in the PSA that we want from the seller. 

If not, try googling "tax assessor database anytown, nh"Understand that tax assessor records don't keep up with sales on NHdeeds.com, so after you have a name, try NHdeeds for the registry for the particular county, and look to see if the person sold it yet or not.