The city announced in December that it was in the process of buying 17 cluster-site buildings. It was later revealed by The Daily News that the buildings were owned by the Podolsky brothers. Mr. de Blasio said then that the negotiations would be delayed while the deal was reviewed; the city later determined that it could proceed.

The city at first said it might use eminent domain to seize the properties but ultimately worked out a deal for their purchase.

A review in 2017 by the Department of Housing Preservation and Development first set the total value of the 17 buildings at about $50 million. But Mr. Banks said that review was not suitable for an eminent domain proceeding, which is intended to capture the value of the properties’ highest- and best-use potential, and a professional appraisal by Metropolitan Valuation Services later estimated the value at $143 million.

City officials said that a “reputable independent appraiser” had prepared an “evaluation for potential condemnation that was consistent with the correct legal standard, so there was no need for another appraisal.”

But Jonathan Miller, the president and chief executive of Miller Samuel, a real estate appraisal company not involved in the transaction, said that it was typical in comparable situations to get more than one appraisal.

“We do a lot of litigation, arbitration, mediation, and there’s almost always multiple appraisals,” Mr. Miller said, adding that if two appraisals are far apart then a third would typically be called for, to ensure that “no money was left on the table, or that a party ended up paying much more than what something is worth.”

He said that the large gap between the Housing Preservation Department estimate and the professional appraisal was a cause for concern, and “with that kind of disparity I would think that would necessitate more than one alternative valuation.”