Preeti Sharma, a 36-year-old information technology manager in Princeton, N.J., signed up for Experian’s monitoring service when she and her husband were seeking a mortgage and worried about surprises that could increase their interest rate. “It brings in another angle that you don’t think about on a daily basis,” she said. Some, including Ms. Sharma, stick with the service afterward.

“Consumers just have an insatiable appetite to know what other people know about them,“ said Don Robert, Experian’s chief executive.

But many customers who sign up for credit monitoring quickly drop it. Michael Schwartz, 63, a retiree in Little Silver, N.J., canceled his Experian subscription after he realized he was paying a charge for a tool he didn’t need. With his house and cars paid off, and his children no longer in school, “it’s not really going to be critical to check credit on a monthly basis,” he added. Experian declined to provide turnover figures, but it said the average enrollment of a monitoring subscriber was under a year.

That is one reason its growing library of commercials is critical to replenishing its subscriber base and revenue, especially among the younger demographic profiled in the ads.

Philip Neustrom, a 25-year-old software engineer in San Francisco, canceled the Experian service after paying six months of $14.95 monthly fees and never using the monitoring. “I knew they had roped me into this thing after I started getting these e-mails,” he said. It took him a while to get around to canceling, he added, because he was busy and “there are only so many things you can do in a day.”

John Ulzheimer, who spent 13 years working for two rivals, said companies like Experian counted on consumers behaving this way. “It says it’s free in the song, but if you don’t cancel, then you start getting hit with a very nominal fee,” he said. “Consumers are busy, and studies have shown that they don’t do a very good job scouring their credit card statements. And they’ll generally discount a charge that is very low.”

‘A Big Moneymaker’

All of this has been good for Experian. At a time when many other financial services firms were struggling, revenue in its consumer credit business grew 20 percent in North America during the 12 months ended March 31. Experian said sales grew about 10 percent in the six months that ended Sept. 30 compared with the same period last year.