At the end of The Maltese Falcon, Sam Spade turns in Brigid O'Shaugnessy despite the two of them being lovers. What anyone would have done in his place is up to the individual, but as for the question of whether or not this act is consistent with Sam's character is a hard one to definitively answer, given how complex Sam Spade is. He toes the line between right and wrong constantly, but if there is one thing made clear, it is that Sam takes his job as a private eye seriously. This fact is what suggests his behavior remains consistent in this final scene.

Sam claims he is turning Brigid in to avenge his dead partner Miles, who Brigid murdered. Even though he disliked Miles, he feels a professional obligation to bring his killer to justice. It is true that the reader might find such a claim suspect, perhaps even a cover-up for Sam's own self-interest. After all, it is in his best interest to turn Brigid in: she's a schemer, a criminal, and bad for his private detective business. To keep her around would make him appear just as corrupt as any of the authority figures in the city. Sam Spade is nothing if not pragmatic. He knows what he has with Brigid is not worth risking his own neck over.

And yet, Sam's earlier behavior in the novel does support the idea that his actions are consistent with his earlier values. While Sam is willing to bend the rules, he only does so to best serve his clients. He cares about his profession, even if he does get his hands dirty sometimes in pursuing it, and Miles is part of that professional world he treasures. So ultimately, his actions at the end of the novel are consistent with his earlier behavior because he is shown to take his job seriously.