Complaining about "kill stealing" in an instance that continually spawns new opponents... that's so "not an issue" it's not funny. Really? /sigh I can see it being "more" of an issue in a RES where you are sitting waiting for targets much more often, and they are more varied (in my experience), but still it's a first world problem.
Seriously, I made 124,000 credits in about 10 minutes in a CZ, so what was one kill worth, 10k? And that's solo, if you are winged it's going to be less. And how, exactly, are you supposed to tell who has what targeted? Unless you stop what you are doing and try to see who's little white lines are going in what direction, then target each ship and see if i's a CMDR, then check... oh, sorry, I've fallen asleep
It's a WAR ZONE people, it's MEANT to be manic! If you've got time to do that sort of stuff you aren't playing the game. Might as well play Solitaire. So just target the next one and get on with it. Who cares?
There are going to be more targets than you can kill even if you stay there all night. Having said that, if I went to a CZ or RES zone and there was already a wing there then and I didn't get an invite I would drop to either solo or my own little private group with just me and a mate in it. Just so I don't shoot someone by accident. But I've only been in one zone were there was anyone else, and we teamed up. I really enjoyed it, looking forward to the next one. Just need to shift this +10GMT time zone so I can be online with more people, seems to be very few players this side of the planet.
On the subject of targeting other CMDRS - I chose the Mobius group because I don't want shooting by other players when I don't expect it who have a ship that massively outclasses mine. NPC ships are all "kill-able" with my Vulture, so I can handle being shot at by any of them. I wouldn't intentionally target another CMDR in a CZ, and I certainly wouldn't blow them up if they were running away. I want to spend my time in the CZ blowing up the NPC's, not end up back at a station, paying out my credits, and then wasting my game time getting back to the action.. all because of a click on someone's joystick ? Nah, not for me.
So many of us, not enough NPC targets, so I suggested to start shooting each other. 
It was like a hungry dog - plop, plop, plop, six NPC's spawned - pew pew pew...neeeext 
I say..if u can shoot and kill, do it, credits will not make themselves u know, no etiquette needed in this situation 
