If Motor-Runner is killed before this quest is received, it will automatically fail.
If you kill all the Fiends in Vault 3 before you see Motor Runner, he will not attack you when you go in his room, even if he appears as a red dot on radar. He will initiate dialogue and you can complete dialogue with him.
If Don Hostetler's wife is dead, then the Courier cannot deliver the mildly suspicious package to him for Diane. Rather than starting dialog, he will merely threaten the Courier.
It is impossible to complete the quest (and therefore learn the Khan trick) without passing a Science check of 50.
Diane won't hand out the Great Khan simple armor to the Courier, if he already has any Great Khan armor in the inventory.
PCPlayStation 3Xbox 360 If you talk to Jack first, you can immediately teach him the recipes, but this will result in the quest becoming stuck.
PCXbox 360 If the quest Still in The Dark was completed and you just went on a rampage in Vault 3 and left, then attempted this quest the radar indicates Jack is hostile but you can still talk to him as if he isn't. The dialogue received is "I was just leaving now" and the mission ends.
PlayStation 3Xbox 360 If you enter Vault 3 without having started Aba Daba Honeymoon, kill all the Fiends, engage Motor-Runner in conversation and then leave, returning when attempting the quest results in Motor-Runner having no dialog options to complete the quest. Killing Motor-Runner will remove the mildly suspicious package from your inventory.
Xbox 360 If you have started Still in the Dark and you have already came and got the reverse pulse cleaner from Vault 3 without making the Fiends or Motor-Runner enemies, Motor-Runner will give only normal Fiend greetings instead of the greeting for the package.
Xbox 360 Starting this quest after starting the unmarked quest to kill Motor-Runner makes it impossible to complete. No dialogue is possible with Motor-Runner after getting the note to kill him from Hsu, making it impossible to sell the suspicious package. You must do this quest first before ever talking to Hsu.
Xbox 360 If you enter the vault before starting Aba Daba Honeymoon, do not pass the speech check, and exit the vault, the Fiend by the vault entrance will not engage in dialog with you, even if you are wearing Great Khan faction armor. This will make it impossible for the Fiend by the vault entrance to tell the other Fiends to not attack you, and you will have to fight your way to Motor-Runner.