Many times on new construction, condo conversion projects, or land being broken off from a larger parcel, the listing agent either estimates (makes a calculated guess) or indicated that it is to be determined (TBD). Until the town or municipality evaluates the new property and assesses it for tax purpose, you will not know what the actual taxes are going to be. In this case, where you believe the estimate is significantly below what you are seeing on similar properties, I believe it would be wise to assume that a year or so down the road then taxes will increase to a level consistent with other area properties.
Just another cautionary note. You mentioned that it was a recent conversion. If you decide to pursue the condo, you may want to ask a few questions upfront to determine whether the complex is warrantable or non-warrantable for financing purposes. Recent multi-family conversions, complexes still controlled by the developer, complexes where one investor owns more than 10% of the units, and complexes with low owner occupancy rates may be much more challenging to get financing on or may not qualify under the program you are currently using. If there is financing involved, It might be prudent to ask a couple of these questions upfront to avoid a potential problem down the road.
Hope that helps!
They may be using the houses pre-conversion assessment as a guide. It is difficult to tell without knowing the property. Kurt is right on with his advice to talk to your mortgage professional to make sure that the unit will meet all of the new guidelines for some of the more popular programs.
I work the Essex County market and would be happy to answer any further questions for you.