This is what Macleans said about it:
“When the Shermans put their house on the market, they did what many rich people do to protect privacy: they used a numbered company as the seller. Sherman had a library to choose from; the one that was chosen listed him as president and his sister-in-law, Mary Shechtman, as a director.
That Sherman had a numbered Ontario company with his sister-in-law named as an officer wouldn’t surprise anyone familiar with his labyrinthine holdings outside of Apotex—ventures that put the test to Sherman’s claim he didn’t care about making money. Relatives pop up in the records of Sherman’s non-Apotex ventures held through “Sherm”-prefixed companies—including Shermco Inc., Sherfam Inc., Sherfam Industries Inc., Sherfam Holdings Inc.—as well as Bernard C. Sherman Limited and numerous trusts and private foundations. The Shermans’ real estate holdings—apartment buildings, condos, commercial properties, rumoured private islands—were held via Sherfam Inc., Signet Realty and Weston, Fla.-based Sherm Realty, as well as trusts.”
Barry and Honey Sherman murders: Inside the lives of the billionaire couple
The listing was featured in Toronto Life just before the murders and clearly identified the Shermans as the owners, so I don’t fully understand how privacy was the reason for listing it that way.