How to verify that a property is a Muti-family

[Tristan Chicklowski]

I was talking with a seller about a 4/2 muti-family. It had an unusual breakdown.  the 1st/2nd floor is one unit  (3/1) the 2nd unit is a 1/1 in the basement kinda. Have not walked the property yet. I don't want to go out if it in not officially a 2 unit. 

So a a short story to a shorter question, "How to verify that a property is a Muti-family?" I think i would be ether the tax assessors, or building department?

I'm out of Massachusetts 

Thanks for all your help!