Satan uses whatever means necessary to keep the lost from finding the truth. Satan co-operates with false religions, which he himself has founded to deceive men. He heals people without their faith in Jesus and His finished work on the Cross. He gives signs and wonders and miracles to keep the unsaved believing that it is God who is doing these things. Such people naturally think they are in the TRUE RELIGION. Satan has won their souls with his shows of power. Demons can go out and come back into a person of their own accord.(Mt. 12:43-45). Satan gives power to his duped followers, thinking they are doing the works of their Father, God. When they are doing the WORKS of their real father, satan. Exorcisms, prayers to the dead, apparitions of Mary, wafers and wine turning into the body and blood of Christ, etc. The "signs and wonders" meant to deceive. And it's working very well.
Neither the account in Matthew 12 or Luke 11 have the Pharisees casting out demons. The crowds saw Jesus cast out demons and wrongly concluded that if the demons obey His command He must be their ruler. Jesus refuted them.
What we can learn from these versus is that demon possession is real and that casting them out is an act of mercy, one of the fruits of the Spirit. That you would ascribe them to Satan only speaks to your motivations.