Beepi began with a lemon of a used car. A few years ago, Ale Resnik, who was then at business school at the Massachusetts Institute of Technology, bought a 2010 Jeep Liberty from a dealership. The car caught fire while his wife was driving it and the dealer didn’t want to take it back. To Mr. Resnik, the failure seemed out of step with the way he shopped for most goods; it lacked transparency and consumer friendliness.

When Mr. Resnik began investigating the auto sales industry, he found that more than 90 percent of American car buyers consulted the Internet for purchases and a rising number of people worldwide say they would buy a car entirely online. According to a study by the research firm Capgemini, about a third of Americans and two-thirds of Chinese who were asked said they would buy a car over the web. To Mr. Resnik, the latent consumer interest was a starting point, and along with a friend, Owen Savir, he set out to create a system to bring to car shopping all the conveniences we’ve grown used to with other online purchases.

“We just thought that the car market was broken,” Mr. Resnik said.

At the core of Beepi’s business model is a pricing trick. There are three relevant prices for any used car. The trade-in price, which is what a dealer will give you for your car; the private sales price, which is what you can get if you sold it directly to someone else; and the retail price, which is the price the car will command at a dealership. Dealers pay the trade-in price for vehicles and then sell them at the retail price. On some cars, that spread can be worth 50 percent.

Beepi thinks it can make a profit while operating within a tighter pricing band. When you list your car with the site, the company’s pricing algorithm, which consults data on historical car sales in your area, offers a price at least $1,000 more than you can get by trading in your car at the dealer. That is still less than what you would get selling privately, but Beepi’s price is guaranteed. If your car doesn’t sell within 30 days of listing on Beepi, the company will buy it from you.

On the other side of the transaction, Beepi sells cars at prices lower than comparable certified used cars at dealerships. It can do so, the founder says, because its overhead is lower — it doesn’t have to maintain parking lots to house cars, because the vehicles stay with the sellers until they are sold. Also, because it buys and sells cars over a wide area — currently, any city in California and Arizona — it can take advantage of supply and demand disparities in different regions. Finally, Beepi caps its own fee at 9 percent, depending on price and demand (it will take as little as 1 percent).