Don was right in that SOMEONE would be willing to buy his place as empty and sad as it appeared.

the realtor was right in that showing the place in such empty and sad condition made it more difficult for her to find a buyer.

and most importantly the realtor was right that the place was empty and sad. and w/o saying it she said and Don saw that the apartment was a reflection of his life - great exterior ("the lobby is nice") but ultimately empty and sad.