Answer:
If Sandy's opinion is true, then it means Westing is out to get his killer revealed.
He would do this to catch his murderer, to find the culprit responsible for his death.
Step-by-step explanation:
Ellen Raskin's "The Westing Game" revolves around the story of an old man Westing's death and the subsequent will that he left, with the declaration that he was murdered. The story follows the 16 heirs of Samuel Westing and their game that will ensure the winner will get the inheritance.
When Sam Westing died and he declared in his will that he was murdered, most probably by one of his 16 heirs, he proposed a game that will reveal the identity of the killer. So, if Sandy's opinion that "Westing is out to get somebody from his grave" is true, then it means Westing wants to get his killer.
He would be out to get the killer because he is the one who murdered him.