GLITCH 1:
1. Get a guy whose body you want to dupe.
2. Knock him unconscious
3. Get into his inventory but DON'T TOUCH ANYTHING
4. Wait until he gets back up (stay in his inventory)
5. Have him log out. (stay in his inventory)
6. After he logs out his body will still be there, you can now start taking stuff out during a 30 second time window, and when the body disappears you can no longer take stuff.
GLITCH 2:
Get into a high ping server (usually happened when I logged in a 200+ ping server). There will be a duplication of your character spawned next to you which you can knock out to loot like it was another player. This duplication is called "uknown entity" and eventually disappears if you don't interact with him (or if you kill him).