Did you even try using one? They are so great for leveling, no one sells those to NPC. That doesn't justify stealing others' items. Did you ask for permission to pick them up? Did you pick them up and say "Hey you don't need this right?" You just assumed he was throwing them, assumed they are yours, assumed they are worthless, assumed you are doing nothing wrong.
Seriously GMs, the LEAST you can do is take away the zeny he got for selling the fish. To let him get away with nothing at all is not fair for Reaper at all. As for the "2 lines conversation" that can be amended with the pm chatlog. This guy isn't denying that Reaper asked for his fish back, and if he does, you can check the chatlog.
Quote:- Final rule
Lastly, if by your action(s) or inaction(s) you cause harm or seriously hinder another character's playing experience, punishments may be given according to the severity of the action(s) or inaction(s).
Doesn't this whole situation fall under this rule?
No one got warned. No one apologized. It's like nothing happened at all. If you ignore this and pretend it never happened, don't be surprised if you see Reaper and his friends KoSing him in PVP and this guy quitting because "everyone" hates him. I know I will.