This is a good question you ask. I'm nowhere as good at incisive Bible study as others on this forum, but I will try my best.
In the passage you are referring to, wich I assume is 1 Samuel 18:10, you might notice that Saul had been disobedient to the very specific command of God. God is the Father of Light and in Him there is no darkness, however by the same token All things are subject to Him. God will use everyhing to achieve His ultimate purposes, as He has no limitations.
There are other similiar passages, where God avails or sends evil spirits, but you might notice that there is always a direct correlation between disobedience and the appearance of an evil spirit sent or allowed by God.
and with all the deception of wickedness for those who perish, because they did not receive the love of the truth so as to be saved.
For this reason God will send upon them a deluding influence so that they will believe what is false,
in order that they all may be judged who did not believe the truth, but took pleasure in wickedness.
The dictionary defines delusion as: "A persistent false belief in the presence of evidence normally sufficient to destroy it"
And just as they did not see fit to acknowledge God any longer, God gave them over to a depraved mind, to do those things which are not proper.
By contrast, you may notice that Job, who had been tormented by satan with God's permission, faithfully responds with the following:
"I know that Thou canst do all things, and that no purpose of Thine can be thwarted. Who is this that hides counsel without knowledge? Therefore I have declared that which I did not understand, things too wonderful for me, which I did not know"
Job showed himself to faithful in spite of very grievous circumstances, and even prayed for those who had maligned him. He proved himself obedient to God, even though the Bible states that he was "comforted for all the evil that he Lord had brought on him". In the end, as you know, the Lord restored all of Job's fortunes, and increased his posessions beyond what he had started out with.
Since Scripture must be studied in context and using more than one reference whenever possible, I think it would be safe to conclude from these passages that God is not author of evil. Although God is Love and Love is God, He will allow evil to enter wherever it is allowed. Rebeliousness, disobedince, wickedness, arrogance, etc., all allow Satan to have legal ground in an individual's life. So while it is not God's will that any should perish, the continued disobedience and rebellion of some call for God's judgement. These are good scriptures to bear in mind. Thank you for asking and may you be very blessed as you study.