@Anhtuan Pham are you looking at the assessed value for property taxes?

In my state, I go to the Department of Assessments and Taxation (that's what it's called in MD).

I do not have a whole lot of experience with legal and zoning, but I have been recently acquired a property that has been assessed as a 3 unit for the past 30 years, and the building inspector says is a 2 unit.

How do I assess the arv here? 

I recommend a Post Compliance Assessment Determination (PCAD) every 5 years or so.Here's the law (emphasis added by me):460.100: Duty of Owner(s) of Residential Premises (B) Whenever any residential premises containing dangerous levels of lead in paint, plaster or other accessible structural material undergoes a change of ownership and as a result a child younger than six years old will become or will continue to be a resident therein, the new owner shall have 90 days after becoming the owner to obtain a Letter of Full Compliance or a Letter of Interim Control, except that if a child younger than six years old who is lead poisoned resides therein, the owner shall not be eligible for interim control, unless the Director grants a waiver pursuant to 105 CMR 460.100(A)(3).

Depending on the number of outlets you need to change, you may also have to upgrade the whole house to new code, including upgrade to gfci to all kitchen and bathrooms.So again you may do some of the upgrade yourself if you are knowledgeable about electricity work, but I would definitely ask an electrician to assess and supervise the work.

I agree with your assessment: "hosed". 

@Emily Beatty I am inclined to go with the French Drain guy's assessment even though his bedside manners are deplorable.

(Education on the house is not a secondary component, several guys will just send their contractors out and assess the bids only, thats a move that only works for experienced investors) Good Luck! 

Second Patti's assessment- Moseley is great