Debt Collector is a quest given in the Atomic Wrangler casino. There are three clients you need to obtain caps from: Santiago, Grecks, and Lady Jane. This is given by Francine Garret. She prefers the debtors be kept alive since you can't collect from a corpse, but you are free to deal with the three individuals as you see fit.
Santiago[edit]
Santiago is located within a squatter camp, and can pay through dialogue options. With a speech check, you can obtain additional caps.
Grecks[edit]
Grecks is located within a squatter camp next to the Old Morman Fort, and can pay through dialogue options. If you have sufficient speech, you can also obtain additional caps to cover the debt collection fee, or even the clothes on his back.
Lady Jane[edit]
Lady Jane appears next to the The Strip Gate. She claims that she doesn't have enough funds to cover the debt and refers you to the Broc Flower Cave far to the south east. However, with a speech or barter skill of 40, the lady killer perk or a perception of 7, you can still obrain the money. You can also ask her for other items to pay off the debt.
You won't be able to pick-pocket or kill Lady Jane, and if she refers you to the cave, her bag of caps disappears.
Caleb[edit]
After you you collect all three debts, Garret reports that the previous bounty hunter stole a bunch of caps and fled to The Strip. She wants you to collect his hat as proof.
When you find him in the strip, you may be able to get the stolen caps and hat with a speech check of 40. Otherwise, you will have to kill him to retrieve the hat.
Return to the Atomic Wrangler when once you collect the hat. Upon completion, you will be given the key to Caleb's former room.