There is 3 ways people "eat" and is actually your own doing instead of theirs..
The first way. Is firing your shots into the opponent before they hit you back. Their bullets wont hurt you (in most rooms. Not all) so it can be a way of winning spar by timing, or rushing the shots.
The second way. Is your own delay between you and the other person. When you fire a bullet and it looks like it hits somebody. Thats because they have already dodged it. What you see is their movements just a moment before they dodged. If it looks like they are going between bullets. They most likely are on their screen. Bullets do have their own lag. What you see isnt exactly what the other person sees so you have to keep that in mind. Most of the time good dodging looks like eating.
The 3rd way is actually lagging to the point bullets dont affect you. Like sometimes when the server lags out and you can walk around in pk areas without dying. If a person is lagging in 1 spot bullets wont affect them however melees will. But if the server lags up and affected them there is no solution other than reporting and asking for a staff to disconnect them so they have to reconnect. Or leave the room. I hope that clears up some answers. i may be slightly wrong about the 2nd answer. But the reality of it is you both see something different. You cant blame the other user.