Brandon Wilson is a former armed robber who, after serving roughly a decade in prison, reinvented himself as a successful debt broker. Basically, he makes a living buying and selling old, unpaid debts.

If you want to buy $100,000 worth of old credit card debts for $1,000, or even $500, he’s your man. But he offered another service to his clients as well. For years, before the Dodd-Frank act created the Consumer Financial Protection Bureau — when the industry was still largely unregulated — he was a fixer, a gun for hire. Here is how he explained it: “Part of the package you get of being my business associate or my friend is that I’m gonna protect you from the sharks.”

Consumer debts — be they credit-card debts, auto loans, gym fees, payday loans, overdue cellphone tabs, old utility bills or even delinquent book club accounts — can be bought, sold and even stolen with relative ease. Typically, these loans are really nothing more than a list of names, addresses, Social Security numbers and balances on an Excel spreadsheet. It doesn’t take much for an unscrupulous debt broker to steal such a file or “double sell” it, by unloading the exact same debt on two unsuspecting buyers. When this happens, a debtor may pay off a debt only to get calls from another company demanding payment once again.

This is where Brandon Wilson’s services come in handy.

Mr. Wilson offers a kind of “insurance policy,” as he puts it. A few years ago, when I was writing a book on the debt-collection industry, I sat in on a meeting between Mr. Wilson and one of his clients — a former banker — and heard him explain how he, and he alone, would keep the thieves, hucksters and criminals away: “If you don’t give them a little bit of fear, right — if it’s just the law, if it’s just the attorney general, if it’s just a civil suit — they could care less. So they need someone to go put a stop to that right now. That might not be bashing someone over the head, it might be sitting them down and saying: Look, man, you ever do 10 years in the can? I have. You ever sat there for 10 years waiting for your date? I have. You think you’re getting away with this? You’re not.”