But Flex operates year-round, not just during the holiday season, which suggests there’s another reason for it: It’s cheap. As the larger trucking industry has discovered over the past decade, using independent contractors rather than unionized drivers saves money, because so many expenses are borne by the drivers, rather than the company.

Amazon has rolled out Flex in more than 50 cities, including New York; Indianapolis, Indiana; and Memphis, Tennessee. The company doesn’t share information about how many drivers it has, but one Seattle economist calculated that 11,262 individuals drove for Flex in California from October 2016 to March 2017, based on information Amazon shared with him to help the company defend a lawsuit about Flex drivers.

On the surface, these jobs, like many others in the gig economy, seem like a good deal. But Flex workers get no health insurance or pension, and are not guaranteed a certain number of hours or shifts a week. They are not covered by basic labor protections such as minimum wage and overtime pay, and they don’t get unemployment benefits if they suddenly can’t work anymore. And when workers calculate how much they’re pulling in on a daily basis, many don’t account for the expenses that they’ll incur doing these jobs. “A lot of these gig-type services essentially rely on people not doing the math on what it actually costs you,” Sucharita Kodali, a Forrester analyst who covers e-commerce, told me.

One Amazon Flex driver in Cleveland, Chris Miller, 63, told me that though he makes $18 an hour, he spends about 40 cents per mile he drives on expenses like gas and car repairs. He bought his car used, with 40,000 miles on it. It now has 140,000, after driving for Flex for seven months, and Uber and Lyft before that. That means he’s incurred about $40,000 in expenses—costs he didn’t think about initially, such as changing the oil more frequently and replacing headlights and taillights. He made slightly less than $10 an hour driving for Uber, he told me, once he factored in these expenses; Flex pays a bit better.

Miller’s wife has a full-time job with benefits, so his Flex earnings are helpful for paying off his family’s credit-card bills. But “if I were trying to make this work as a single guy on my own, it would be tough to do that,” he said. His costs might actually be lower than what most drivers spend: The standard mileage rate for use of a car for business purposes, according to the IRS, is 54.5 cents a mile in 2018.

I became an Amazon Flex independent contractor by downloading an app, going through a background check, and watching 19 videos that explained in great detail the process of delivering packages. (I did not get paid for the time it took to watch these videos, and there was no guarantee that I would be approved as a driver once I watched the videos.) The videos covered topics such as what to do when a customer decides they don’t want their order anymore (“Isn’t this customer nuts?!” Amazon asks), and how to deliver alcohol (asking customers how old they are, it turns out, is not an acceptable form of checking ID). Because the videos were followed by quizzes, I actually had to pay attention.