It's still a line I cannot draw with any reliability, but I can now name a few landmarks between which it must pass. Mercy is giving one student a chance, one time. Selling out is erasing history for a whole class of twenty. Mercy is looking deep into your own heart and the heart of the person whose fate is in your hands, knowing the two are inextricably bound. Selling out is deciding on convenience and hearsay.
Mercy is the flip side of justice.
Selling out is no coin at all.