In the first book, Voldemort realizes that Harry has the Philosopher's Stone. He essentially asks Harry to join him. Was this a real offer, or was Voldemort just trying to manipulate Harry into giving him the Stone?
Clearly, Voldemort is ruthless, sociopathic, and self-centered to the extreme; he saw people mostly in terms of their usefulness to him. Clearly, he wouldn't see his word as an obstacle to killing Harry, and he obviously blames Harry for what happened to him. However, he was willing to work even with wizards that disgusted him
(such as Wormtail/Peter Pettigrew, who Voldemort kept around because he was useful, in spite of knowing full well that he was a treacherous coward who wasn't truly loyal to him).
So, on the one hand, Harry was (potentially) useful to him. On the other hand, both him and Harry were eager to get revenge on the other. That being said, was Voldemort actually making a real offer based on Harry's potential usefulness, or was he merely trying to manipulate Harry into giving him the Stone?