Strictly Profitable

Strictly Profitable is an unmarked and repeatable quest in Fallout 3.

Detailed walkthrough
After receiving the Mesmetron from Grouse in Paradise Falls, one has the option of enslaving non-player characters other than the four VIPs required to complete the quest Strictly Business. For every slave that is captured and sent back to Paradise Falls, Grouse will pay out 250 caps, and will hand over a new slave collar to continue the "recruiting." He also sells Mesmetron Power Cells at the steep price of 200 caps per 10 rounds. It's possible to offset the high price if all 50 rounds he initially gives out are carefully utilized since he also pays out caps for turning in the VIPs.

Rewards

 * 250 caps per slave.