If the Vault Dweller chooses to kill Razor and/or make the Blades hostile, the Gun Runners become hostile, preventing access to this quest. So it's best to wait until completion of Exterminate the deathclaws.
Bug[]
After completing the quest, move out of the sector and run back to the Gun Runner's territory in less than 2 days. Then you may be able to gain 1000 exp each time you do so.