Strictly Business is a quest required to enter Paradise falls without incident. When you first approach the entrance, Grouse will stop you, but through dialogue options, you can convince him to give you a list of four VIPs that you want captured. To complete the quest, capture all four VIPs.
He gives you a slave collar, a mesmetron, and four different targets. To get the reward for each slave, you need to ensure they safely reach Paradise Falls; the best way to do so is using fast travel.
You can bypass the quest either violently or using a speech check and 500 caps.
Arkansas is a sniper located in Minefield, who was causing problems for the slavers.
Minefield is a ghost town with a lone sniper and is filled with landmines. There are a few parked cars filled with gasoline that are used as an initial line of defense; he will shoot these cars when you move past them, even if you are invisible to him.
The best means to get close is to use a stealth boy. Crouch and sneak up the stairs, and hit him with a head shot with the mesmetron. Put the collar on him.
Susan Lancaster is a prostitute working in Tenpenny Tower. To grab her, you may want to wait until night time, and follow her to a room with one of her clients. When the client wakes up and leaves, use the mesmetron.
Note that some tower residents may become hostile if you are near her while she is fleeing. Wait a few minutes before heading to the first floor (or use a stealth boy if necessary.)
Flak, who left the slavers to start a new life, runs the Flak & Shrapnel shop in Rivet City.
At times, he heads to the end of the corridor leading to the Science lab, but is also known to take smoke breaks on the flight deck alone.
Red from Big Town is the doctor in the clinic that managed to keep the slavers away. However, she is held in the Super Mutant prison to begin with (and is easy to deal with at that point.)
If you rescued Red, you'll have to capture her from the clinic.
While not part of the quest, you can capture any humans you want with the mesmetron and slave collar. However, the mesmetron is not perfect, as some are immune to the disabling effect, and others will have their head explode (e.g. Talon company mercenaries).
However, if you capture an individual in a random encounter, you may need to escort that individual all the way to paraside falls.
If you run out of batteries, you can purchase 10 more from Grosse for 200 caps each.