It wasn’t all that long ago that savvy consumers were reluctant to buy refurbished electronics. As recently as 2012, MacWorld called the world of refurbed iPhones “potentially shady,” while one Lifehacker writer cautioned readers that her “personal experience buying refurbished gadgets has been a horror story.”

But recently, there’s been a surge in people buying refurbished smartphones. And tech experts have changed their tune: CNET’s Rick Broida famously declared that shoppers should opt for a refurb Apple product over a new item “every time.”

Factory-refurbs with manufacturer warranties can be an affordable, reliable option — and demand is growing.

Our friends at DealNews have long been fans of the noble refurb. When backed by a proper warranty and a return policy, a refurbished smartphone can save you a ton of cash over a brand-new model. But even knowing what a great deal a refurb phone can be, we’re still a little surprised at just how popular refurbished smartphones have gotten recently. So what’s behind this shopping trend?

Refurb demand to double by 2017

A recent Gartner survey found that the demand for refurbished phones will grow to 120 million units by 2017, a business that will be worth about $14 billion. This is up from 56 million units in 2014. In essence, the refurb market is expected to just about double in only a few years’ time. According to Gartner, over half the people buying refurbs are getting a new phone because they want access to new features, or they “just want” that new device feel.

Those figures are in line with trends that resale services like Gazelle are seeing. According to Gazelle’s Kevin Walther, market research has found that about 40 million U.S. consumers would consider purchasing a used smartphone. Since Gazelle launched its certified pre-owned smartphone store in October, the company has seen month-over-month growth of about 20%.

Read more: Why your next phone might be a refurb – TechSpot.