Sometimes it is very obvious coz the battle is too easy. Someone will usually say "Hey! did you just kill so-and-so" and when asked "politely", the spoils of battle can be shared.
However, what does one do if you have a full battle, collect the spoils and then someone says "Hey, I was killing so-and-so - I want whatever they dropped". Sure it can lead to interesting role-play but in the end, what does one do - hand over the loot
 or tell the other person to find a cliff and jump off it
  or tell the other person to find a cliff and jump off it 


 But to answer your question: it really depends on which char you killed the creature and which char was fighting it as well. Due to rp some classes cannot negotiate with eachother (however, you can make deals through ooc ), but my opinion on full battle fights: you killed it, you earned it. They did not make enough damage to kill the creature or even harm it, but you did. You did more work, so it's your loot.
 But to answer your question: it really depends on which char you killed the creature and which char was fighting it as well. Due to rp some classes cannot negotiate with eachother (however, you can make deals through ooc ), but my opinion on full battle fights: you killed it, you earned it. They did not make enough damage to kill the creature or even harm it, but you did. You did more work, so it's your loot.