In Sin City Josh Hartnett portrayed the Salesman. It is assumed that he killed the hooker "Becky" by the end of the movie. I reviewed this Sin City movie, but couldn't find a logical reason why she becomes the salesman's target. Is there an explanation even in the Sin City story series? (As for the movie, I could only think that they put the Salesman story at the end, to give the Sin City an interesting ending)
My initial take was that he's a hitman hired by the girls from Old Town to punish Becky for betraying them:
Then Dwight McCarthy discovers that Jack Rafferty was a cop and Becky realizes that the cops and the mob will go to war with Old Town now that the Truce was broken. When Dwight and Miho are packing the bodies of the five men into the car, Becky asks Gail if she can go home because the blood is making her sick. Gail tells her not to talk to anyone even her own mother.
Becky leaves and uses a pay phone when Dallas and another girl comment that she is not to use the phone. Becky tells them she is calling her mom just to hear her voice. Dallas leaves and Becky then calls Wallenquist to make a deal with him to let her and her mother live.
However, considering that The Colonel (a.k.a The Man a.k.a The Salesman) is part of Wallenquist Organization, that doesn't make much sense. I suspect he's just there to clean up "loose ends": Becky's betrayed her own people, so why wouldn't she do the same to the Mob? She's expendable to them.
The comics tell a different story, in which Becky is killed along with the other Mob members when they fall into the girls' trap:
Back at Old Town, Gail has been ambushed and kidnapped by Manute, who has survived the previous assaults of Dwight and Miho. Gail is tortured but refuses to "facilitate" the process of surrendering Old Town. It becomes clear that Becky had sold out Old Town for money and her mother's safety. Gail bites and rips a chunk off of Becky's neck in anger, vowing that she deserves worse.
As the gangsters prepare to further torture Gail, and kill Becky, an arrow shoots through one of the henchmen with a note prompting a trade: Jack's head for Gail's life.
As Dwight stands alone in an alley outside the gangsters' building with the head, outnumbered and outgunned, the trade is made: Gail being freed and the head, now bandaged up, handed over. Becky questions why the head is now bandaged when it wasn't before. Dwight then triggers the grenades stolen from the last mercenary, exploding the head.
The gangsters now realize they are in a trap as the girls of Old Town reveal themselves, heavily armed also, on the roof. Before any defensive measures can be taken, the men and Becky are gunned down.
Note how the Mob was going to kill Becky anyway.
Becky was expelled for her betrayal to the other prostitutes. Her mom's life was threatened. In the end you see her meet "The Salesman." In the beginning she is referred to as "The Customer." Becky, as the customer, hired the hitman to kill her to protect her mom and because she was suicidal, but didn't have the courage to take her own life.
That is why in the beginning he said he was watching her for days. This is in reference to how people would hire hitmen to kill them as a form of suicide back in the 1920s during the Great Depression. Then he mentioned he would cash her check in the morning. The check being the payment she gave him to kill her.
In the film you will noticed a lot of people wearing red. All those who wore red were marked to stand out as commonly used symbolism for survivors until the end, but with a twist, they each died on their own terms but also to protect someone.
Becky via suicide to protect her mom. Cartigan via suicide to protect Nancy. Marv accepted the chair to protect Wendy and her fellow prostitutes.