Dispose of merchant

Dispose of merchant is a side quest in Fallout. It is given by Decker and requires the Vault Dweller to kill the merchant Daren Hightower and his wife for refusing to deal with the Underground.

Detailed walkthrough
To receive this quest the Vault Dweller must either speak to Lorenzo at the Friendly Lending Company and ask him about Decker, or have killed Killian Darkwater for Gizmo. In the former route, Lorenzo will tell the Vault Dweller who to go to for work. The Vault Dweller then ought to tell Kane in the Maltese Falcon that they are looking for a job and mention Lorenzo's referral. In the latter route, directly talking to Kane will reveal that he knows about the Vault Dweller killing Killian and offer a job. You can bypass the dialogue with Lorenzo and not have to exterminate Killian by simply going to Kane and doing the following: initiate conversation with Kane then choose "I need to talk to Decker". Kane will ask why and then you must say "That doesn't concern you. Now take me to him." If you fail this check then reinitialize dialogue with Kane and when prompted for a response say "I'm sorry, I just wanted a job." He will then take you to Decker.

After accepting the quest the Vault Dweller can collect their $500 down-payment from Kane. Then they need to go to the southwest exit grid in Downtown of the Hub. This will take them to the Heights. The Hightowers live in the building in the middle of the section. The Vault Dweller should talk to the guard outside the door and mention that they're running late for an appointment to get into the mansion.

Then it's just a matter of walking into the merchant's bedroom and opening fire. Both Daren and his wife need to die. Talking to Mr. Hightower will result in the Vault Dweller being kicked out, so just shooting the couple is preferable. In response, all five of the guards will come running inside. They are moderately well armed: three have 10mm SMGs, one has a Desert Eagle, while Leon has a 14mm pistol. Since Decker demands the elimination of any witnesses, they need to go too.

Another way to get the quest done is to come at night (after 7PM), and promising to go away when the guard hassles the Vault Dweller. Instead of leaving, the Vault Dweller should go around the house clockwise, wait just around the corner so that the guard in front of the door sees them (keep facing away until guard turns). When the guard passes around the corner, the Vault Dweller should run back to the door, open it, then close it once their companions are also inside, but before the guard returns. The Vault Dweller can now kill Hightower and his wife without the guards noticing, as long as they don't enter the guards' field of view (sight) on their way to the exit grid. There isn't any particular advantage for doing so, except if they just want to avoid bloodshed, or are weak in combat.

The Vault Dweller can then head right on back to the Maltese Falcon and speak with Kane to get the reward. Hub Cops will not turn hostile.

Yet another way would be to sneak into the back of the house at night as mentioned above, and shoot the Hightowers through their bedroom window. If you're lucky to get them lined up right, using a burst fire weapon or whatever character skills to get them both in one round might let you pass unnoticed by the guards.

Take down Decker
After getting this quest from Decker, the Vault Dweller can choose not to do it at any time and rat him out to the Hub Cops, Sheriff Justin Greene specifically. He'll request the Vault Dweller's help in raiding the Maltese Falcon and stamping out the Underground. One can even do this after completing the quest and receiving its reward, as long as a Charisma/Speech check is completed.

Rewards

 * 500 XP
 * 3000 caps
 * -2 Reputation
 * Decker's next quest: Dispose of Jain