Many Catholics do not know what they are supposed to believe. When you explain the gospel to them they might not realize that is not what they are supposed to believe. After I explain that Jesus died on the cross to pay their fine I show them that if the fine is paid in full why would there be a place in the middle like purgatory. I take people to Luke 17 and show that Jesus only talks about heaven and hell and no other place.
The following are videos that show what they are supposed to believe.