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I'll raise my hand here, from time to time, I do kill steal. Dependant on whether I'm in a good or bad mood depends on how it's received though. I'll only EVER kill steal someone who takes either the entire spawn (Off the top of my head, the only spawn this small I can think of is Jack The Hammers/Drillers) or if they take the 'best part of the spawn' (Like if two AoErs take small and captain carriers, leaving only the normals with damn projectiles). If I'm in a good mood, I'll ask them to leave some for me, be patient, wait for a response and possibly leave for a different spawn if they seem like the really need it all. Obviously if they're a bitch about it, I'll just kill steal them until they leave, taking an eye for an eye approach and simply be just as bitchy about the spawn.
Other days, I get annoyed and when it's dead obvious they have more than is neccesary (i.e an area totally devoid of mobs) then I'll walk through the empty spawn and simply take one. Then they'll say something like "Don't KS nub" or "No ks pls". By this point I'll be quite irate anyway, so I'll just continue until they get the point.
Call it harsh or whatever you like, I'm aware there are several other servers to choose from. But most of the time the AoEing is excessive and not neccesary, Imo, if you can tank 3/4's of the spawn, you should be moving on or consider lowering your stamina to allow for some power.
At the end of the day, if Kill Stealing happens, it's someone's fault. But some AoErs need to learn that sometimes the fault is theirs. I'm not saying that to anyone in particular so don't take it as a flame, but when people have different views on AoE (Like another 1v1 character could claim that an AoEr that can tank 3 of the 'next up' mob should move on) you're bound to get different 'rules' as to whether they'll want to kill steal. Odds are that with the game's population, you won't be the one to blame if you're conscious of what this topic is talking about, but if you're getting Kill Stealed a little too often it's worth considering that you may be calling it on yourself.
That's my two cents
For the 'tl;dr' bitches, I'll summarise: Kill Stealing happens, either the aoer or the 1v1er is to blame but it can be both. Be sure to know whose fault it to avoid potential KSing.
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Edit: I'm probably gonna get flamed/stereotyped for being a Blade a.k.a the noob class, I'd like to point out I can be polite most of the time and respect most of the etiquette in game. Kill stealing is just an area that becomes hazey to judge on whether it's justifiable because of conflicting views.