Do devils always lie, or do they sometimes speak true things?
Mat 8:28-29
(28) And when he was come to the other side into the country of the Gergesenes, there met him two possessed with devils, coming out of the tombs, exceeding fierce, so that no man might pass by that way.
(29) And, behold, they cried out, saying, What have we to do with thee, Jesus, thou Son of God? art thou come hither to torment us before the time?
Luk 8:27-28
(27) And when he went forth to land, there met him out of the city a certain man, which had devils long time, and ware no clothes, neither abode in any house, but in the tombs.
(28) When he saw Jesus, he cried out, and fell down before him, and with a loud voice said, What have I to do with thee, Jesus, thou Son of God most high? I beseech thee, torment me not.
Act 16:16-18
(16) And it came to pass, as we went to prayer, a certain damsel possessed with a spirit of divination met us, which brought her masters much gain by soothsaying:
(17) The same followed Paul and us, and cried, saying, These men are the servants of the most high God, which shew unto us the way of salvation.
(18) And this did she many days. But Paul, being grieved, turned and said to the spirit, I command thee in the name of Jesus Christ to come out of her. And he came out the same hour.
Just because a spirit speaks something which is true or comes true, does not mean that it is a righteous spirit. Devils lie, but not always.