Hammond Residential GMAC Real Estate, which operates 12 offices in Massachusetts, has been sold back to Saul B. Cohen, who founded the company in 1991 and sold it to GMAC Home Services 10 years later.

All 12 offices, staffed by more than 400 sales associates and employees, will continue to operate as Hammond Residential GMAC Real Estate. In 2008, the company had sales of more than $1 billion, according to a statement.

The company operates four offices in Boston (South End, Charlestown, Beacon Hill and Back Bay) and eight in the city’s western suburbs (Brookline, Newton, Wellesley, Weston, Framingham, Concord, Winchester and Lexington).

The offices will be run by Cohen, who will be a franchisee of Brookfield Residential Property Services, owners of GMAC Real Estate.

Separately, it was announced that two Carlson GMAC Real Estate offices in Chicopee and Wilbraham have been acquired by Robert Molta, a longtime real estate industry executive. A third Carlson GMAC Real Estate office, located in North Andover, has been sold to local entrepreneur and real estate veteran George Schruender.

As part of the agreements, each of the three Carlson offices will continue to operate as Carlson GMAC Real Estate and will become franchisees of GMAC Real Estate.