Job titles don’t tell you whether someone is primarily a rent seeker. A lawyer who helps draft precise contracts may actually be helping the wheels of commerce turn, and so creating wealth. But trial lawyers in a country with poorly functioning tort systems may simply be extracting rents: They can make money by pursuing frivolous lawsuits.

Image A scene from “It’s a Wonderful Life” that presents two types of bankers. Mr. Potter, seated, played by Lionel Barrymore, pursues only personal gain, while George Bailey, played by Jimmy Stewart, helps workers in his community buy homes. Credit... Bettmann/Corbis

In this respect, finance is a vexing industry. Take arbitrage — a common way to make money in finance. Find a stock that should be valued at $15 but that is trading at $10, buy it, wait and hope. You might assume that stock markets are just a big casino, in which skilled traders extract money.

But arbitrageurs can create value, and stock markets can play an important social function. They determine which companies receive capital cheaply and which pay a heavy price for it, determining where factories are built, which retail stores are expanded and where research and development happens. Mispriced stocks can mean misplaced investments. Arbitrageurs help get the prices right, and that’s important.

Still, arbitrage is valuable only to a point. It has a gold rush element with prospectors racing to get to the gold first. While finding gold has value, finding gold before someone else does is mainly rent-seeking.

The economists Eric Budish at the Booth School of Business and Peter Cramton at the University of Maryland, and John J. Shim, a Ph.D. candidate at Booth, have shown in a study how extreme this financial gold rush has become in at least one corner of the financial world. From 2005 to 2011, they found that the duration of arbitrage opportunities in the Chicago Mercantile Exchange and the New York Stock Exchange declined from a median of 97 milliseconds to seven milliseconds. No doubt that’s an achievement, but correcting mispricing at this speed is unlikely to have any real social benefit: What serious investment is being guided by prices at the millisecond level? Short-term arbitrage, while lucrative, seems to be mainly rent-seeking.

This kind of rent-seeking behavior is widespread in other parts of finance. Banks sometimes make money by using hidden fees rather than adding true value. Debt collection agencies may use unscrupulous practices. Lenders to poor people buying used cars can make profits with business models that encourage high rates of default — making money by taking advantage of people’s overconfidence about what cars they can afford and by repossessing vehicles. These kinds of practices may be both lucrative — and socially pernicious.

But finance need not be this way. George Bailey, the protagonist in the classic film “It’s a Wonderful Life,” was a banker. When he was reluctant to take the job, his father explained to him: “You know, George, I feel that in a small way we are doing something important. Satisfying a fundamental urge. It’s deep in the race for a man to want his own roof and walls and fireplace, and we’re helping him get those things.”