Here are three of the week's top pieces of financial insight, gathered from around the web:

Special car warranty offer? Skip it
Extended car warranties are too often "a bad deal," said David Lazarus at the Los Angeles Times. "As I frequently tell consumers, if insurance helps you sleep at night, it's probably worth it." But generally speaking, service contracts don't deliver enough bang for their buck. "A 2013 survey by Consumer Reports found that 55 percent of people who purchased extended car warranties never used the coverage." Even those who did saved about $837 on covered repairs, far less than the $1,500 median cost of the coverage. You should steer clear of "coverage pitched by marketing letters or robocalls." Many car dealers "sell details of extended warranties to data brokers, which in turn sell them to others," giving salesmen that information about your car.

Robinhood's turn in the hot seat
Lawmakers took aim at the chief executive of Robinhood at a hearing last week, said Nathaniel Popper and Matt Phillips at The New York Times. "Members of the House Financial Services Committee grilled Vlad Tenev," who was called in for questioning along with other major players in last month's GameStop trading frenzy. Several representatives accused Robinhood of profiting from trades that aren't really free, because the brokerage is "paid by Citadel Securities and other hedge funds for directing customer orders to them." Citadel in turn makes money by "exploiting tiny differences between the buy and sell prices" of trades on the Robinhood app. Tenev disputed the lawmakers' claims, saying that Robinhood "doesn't answer to hedge funds" and that its customers have earned $35 billion on their investments.

A tax debt yields a surprise profit
An online bank customer received $47,000 cash back after paying taxes with a debit card, said Felix Salmon at Axios. "Thanks to a quirk of the U.S. payments processing infrastructure," some taxpayers are taking full advantage of their 1 percent rewards card. A customer at an online bank called Jiko did so recently, using a Discover debit card to make a $4.7 million tax payment. The bank, which offers 1 percent cash back on all debit card purchases, handed the customer a $47,000 windfall. The IRS got its full $4.7 million, while the government's payment processor "had to pay more than 1 percent of the transaction back to Discover and thence to Jiko," which passed it on to the customer. "This is probably not going to last," said Jiko CEO Stephane Lintner.

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