At the end of Act II, John Proctor gets the idea to use Mary Warren to prove that the girls are lying. His plan backfires in Act III when he actually takes Mary Warren to the courthouse to reveal that the girls had been lying. Abigail had turned around the story and blamed Mary Warren, who then in turn blamed Proctor and accused him of dealing with the devil. This shows that all of the girls are lying simply to save themselves, even in court.
But who told Giles?
Mrs. Putnam accuses Rebecca Nurse of being a witch because most of the children she delivered for her died early into the pregnancy. Putnam uses the witch trials and the rising paranoia of witches to get rid of Nurse.
The girls say you're a witch, so you must be a witch!
Giles refuses to confess to whether he is a witch or not so he can die a Christian and allow his family to keep their property. Since he won't confess, he is killed, which would have been the same outcome if he were to tell them he was not a witch.
Aaaand, I'm going to die.
The scene where Giles accuses Mr. Putnam of using the witch trials to gain more land shows greed because Putnam is simply using his daughter in order to take land from other farmers. The reason that Giles doesn't give away his informants name is that whenever he mentions a name in court they end up in jail.
Someone told me that his daughter falsely accused a man for his land!
This scene represents how very little work was ever done to prove whether someone was a witch or not. This is an example of the hysteria that was present throughout the play because people in Salem were too caught up in the idea of witches living in their town to ever stop and think that there might be some altierior motives.
He's a witch!
Are you kidding me?!
This shows how Elizabeth Proctor lied in court to save her husband's good name, even though, after his confession to having an affair with Abigail, it had been ruined. This is an example of pride because Elizabeth, a woman known for never telling a lie, lied in court to save her husband's name.