Its only my Opinion...But
It's very Easy to answer this question.
IF you think there is no such thing. Then YOU most likely are a "Kill Stealer."
Blammo
"Just a note: I don't believe there is such a thing as stealing a kill in the main arena, but maybe I am just naive."(Kill Stealer) . porlly never intended to pose a question. Just lookin for moral support.

Foot note: Conclusion drawn in part from the Posters Avator.

Toad
"It would be when you get the kill on an airplane they either shot at and hit, shot at and missed, thought about shooting at, saw off in the distance or was in the MA at the same time they were." (Kill Stealer) .
WldThing
"LOL ive been accused of it once or twice, 1st time in the MA, a fellow countrymen had hit the cons radiator, so the con started running away, and i know the ally couldnt catch him so i dove down and killed him and got called a kill stealer."
Second time was in a special event, where some of the JB's started screaming at me on vox in a furball where i apparently wasnt invited to come and steal their squaddies kills..."(Kill Stealer) .
WldThing
"It's war all is fair, just squelch em and move on Blammo"(Doesn't Giva Rats Butt if anyone likes it either)
humble
"No such thing....
However many pilots exibit bad form...often failing to allow cripples to live long enough for you to catch them and kill them...or even worse finishing those who you have elected to only wound...after all it is a game and sportsmanship dictates a valient foe should have a second chance.
Realistically it's simple...if you see it in front of you...shoot it."(Closet Kill Stealer/ Kinda)

)
SlapShot
"It use to piss me off too ...
Fight a guy ... shoot his wing off and as he slowly decends toward Mother Earth, you can see at least 3 or more friendlys shooting at the dead carcass hoping to get the plane to blow up so they get the kill.
Now I look down, and after they have spent mucho ammo trying and sometimes succeeding in stealing the kill, they are low and slow and are bait for the enemy. I then watch them, with delight, get killed and then I drop and kill the enemy ... the key word here is bait ... hehehe.
If you feel as tho you need to kill a plane with no wings, on fire, and headed toward terra firma ... go for it ... there are many more kills just waiting to happen."(Fishing season never closes for this fisherman. "Bait is the key Word Here") Better look up and see from whose Hook you are dangling. Burning/spinning NME Plane or not!

Mini D
"This is Kill Stealing
That should clear things up for you.
MiniD" (Most definitely NOT a Closet KILL Stealer)

Zazen13
"Good rule of thumb I always tell newbies...If the enemy is smoking shoot away, if it's missing it's tail or a wing, leave it alone. Can't tell you the number of times I've seen folks chase wingless/tail-less wrecks to deck firing away"(Advises newbies fairly)

A few hints
If you want to be a Gamey Gamer. Steal away. God knows that many are doing it. I for one never intentionally steal a kill. In fact i have rarely done it on accident.

Its a conscious effort. Quite simple to NOT participate, if you care.