What was unusual about the way the tenants were chosen to live at Sunset Towers in The Westing Game?

The tenants of Sunset Towers were hand-picked. 

The first unusual thing about the Sunset Towers tenants is that the person who delivers the advertisement, Barney Northrup, is sixty-two years old.  He is riding around town hand-delivering letters.  The description of Sunset Towers makes it perfect for the people who get the letters.  For example, there is space for a dentist, a coffee shop, and a restaurant.  Also unusual is the fact that everyone who gets a letter makes an appointment to see the place. 

When showing the Wexlers their apartment, Northrup knows exactly what to say to impress them. 

“You’re really in luck,” Barney Northrup said. “There’s only one apartment left, but you’ll love it. It was meant for you.” He flung open the door to 3D. “Now, is that breathtaking, or is that breathtaking?” (Ch. 1) 

Realtors often say that a place is meant for you when showing it to you, but in this case he means it.  Each tenant was hand-picked, and a letter hand-delivered.  There is an apartment for each of them.  They are Westing family heirs.  However, as we are told, there is just one problem. 

Who were these people, these specially selected tenants? They were mothers and fathers and children. A dressmaker, a secretary, an inventor, a doctor, a judge. And, oh yes, one was a bookie, one was a burglar, one was a bomber, and one was a mistake. Barney Northrup had rented one of the apartments to the wrong person. (Ch. 1) 

It turns out that Sydelle Pulaski was chosen by mistake.  The private investigator who was supposed to find everyone, Otis Amber, found Sydelle Pulaski instead of Sybil Pulaski.  Other than that, everyone was hand-picked by Sam Westing to play the Westing Game.  He wanted to get to know his heirs, and find out what kind of people they were.  Westing was an eccentric man.