When Jerome Debs offered $2.8 million for a Lowell Avenue house and the sellers accepted, Debs seemingly had every reason to believe that he had just purchased his family’s next home. But what looked like a done deal quickly unraveled.

In a city where homes are commanding million-dollar price tags, a dispute between Debs and Coldwell Banker, the real estate brokerage that represented him in the transaction, could have an impact on how the agency does business.