As I was reading Chiefs post on good and evil I kept thinking of Faust so I thought I would check it out a little. We didn’t get to here everything Smocke offered Sayid but it does seem he already claimed his soul.
From the wikipedia page on Mephistopholes
Although Mephistopheles appears to Faustus as a devil – a worker of Satan – critics claim that he does not search for men to corrupt but come to serve and ultimately collect the souls of those who are already damned. Farnham explains, “Nor does Mephistophiles first appear to Faustus as a devil who walks up and down in earth to tempt and corrupt any man encountered. He appears because he senses in Faustus’ magical summons that Faustus is already corrupt, that indeed he is already ‘in danger to be damned’.” 
Mephistopheles is already trapped in his own hell by serving the Devil. He warns Faustus of the choice he is making by “selling his soul” to the Devil: “Mephistophilis, an agent of Lucifer, appears and at first advises Faust not to forgo the promise of heaven to pursue his goals”.  Farnham adds to his theory, “…[Faustus] enters an ever-present private hell like that of Mephistophiles”.  Both Farnham and Krstovic/Lazzardi see Mephistopheles as a worker of the devil who was summoned by the already-damned soul of Faustus. But the Gale Literature Criticism takes him to the next step, almost portraying Mephistopheles as a protector while Farnham displays him as a servant of Lucifer.
Sayid was ripe for the taking/claiming by Smocke. Sawyer would also fall into the category of already being corrupted although I think he is of stronger character than Sayid in the long run.