Unless he is approached by someone with a badge and gun, I would find a qualified Enrolled Agent who specializes in audit or collection issues.

Somewhere searching around on the IRS web site, I found a set of guidelines for auditors on this topic.

The Tax Assessor's Office is responsible for assessing taxes on properties, the Tax Collector's Office is responsible for collecting property tax payments, and the Auditor-Controller's Office is responsible for setting/applying the appropriate tax rates (they also publish this information). 

the local county auditor list + fastpeoplesearch.com + followupboss + opencorporates is a good way to get contacts and find deals. 

The letter indicates that they will certify the unpaid amounts to the County Auditor and it will be added to the property taxes.Number 1.)

MLS can't send you the agent version - only Buyers so you need to find closing date on the auditor site or Realtor.com

Online real estate site like redfin, zillow, and truly will typically have that info (they just link from the auditor's websites).

PM me if you're an auditor and want to verify my numbers. 

As an energy auditor, I get these calls all the time,Popular things are:-extra fridger/freezers in the garage (typically a free or old one they dont realize uses a ton of electric),-Hotwater tanks & Heating (is NG an option) If not look at airleakage and insulation-Failed wel lpumps or sump pumps that never stop running,-Non-Energy star Dehumidifiers,-electric space heaters that get left on or forgot about-A ton of Incidence light bulbsAnd the biggest one, Is typically not the KWH at all, but people switching to other non regulated providers such as ambit who have a habit of slowly creeping up to double/triple the market rate.

I remember years ago when reviewing some tax filings with the IRS, the auditor sat there and ask me how I defined myself, she accepted the investor line with the properties, while I was in the lending buisness and bought/sold mortgages.