They're actors hired by coworkers - revealed at the beginning of the fil
Its not a spoiler if its the actual plot revealed in the first 15 minutes.
They don't want him to lead their company since he's depressed and dumb so they hire actors and a private investigator to film Smith talking to them so they can digitally remove the actors from the cell phone footage (right...) and make it look like he's crazy.
Trailers were extremely misleading
There, I just saved you $30 assuming you would've taken a date and you like popcorn.
https://youtu.be/COqgClha3D0