Was Steven Ever Really a Hit Man? Who is Thomas? (spoliers)

Some people question whether Steven was ever a contract killer at all. I think that he probably was for several reasons.

First, Percival seems to have learned of Steven's profession independently, indicating that he must have sought hit man and been given Steven's contact information.

Second, in their first meeting, Thomas tells him that he (Steven) has been "freelancing again," and Steven replies that he "needed the money because I not making anything working for you." While this is foreshadowing about the real nature of the relationship of Steven and Thomas, it also suggests that Percival is not the first person to employ Steven to kill someone, interfering with his work for Thomas.

Finally, there is the opening sequence, Steven telling the shopkeeper "I am not really father material" and his violent reaction to the rude customer.

That leads to another question, since it is revealed at the end of the movie that Thomas is a figment of Steven's imagination, and the the "work" he has been giving Steven is to hunt down Annie's possible killers, who is the alter-ego that Thomas represents? I think the most likely choice is that he is Steven's father.