(Which is surprising in the Live Free or Die state) While I have no doubt that what you are saying about your personal situation is true, in NH, the situation is quite different.   

I highly doubt they only make $1,500/house bet on average.

When in doubt...

Yet, I doubt they will want to pay so that is fine with me. 

He'd have to demo the sheetrock, put up water proof cement board, and install about 140 sqft of 12x24 tile and frame out 2 stainless steel wall niches.

I will reply but I doubt I will be of much help.Every state has different statutes regarding how certificates are created, acquired, effective periods, minimum certificate age required to apply for a tax deed, certificate expiration age, etc.I recommend that you post what states you are interested in purchasing certificates and hopefully individuals who have acquired certificates in these states will respond.Your strategies will dictate your operating costs. 

. ;-)  When in doubt, only trust the lower of the two.  

I just went through this process and my firewall was approved by they city, but only after I replaced all screws with cement coated fire-rated nails. 

Our town isn't really Airbnb material so I doubt that would work to well.

@John Ratigan   hold your horses this is a loser.. and I doubt you will find a lender to lend you this month as they will run the math and help you realize that the only one making any money on the deal is them..