The iPhone is a great device, but they don’t come cheap and they rarely go on sale. So if you want to buy an iPhone without paying full price, a used iPhone might be your best option. While a used iPhone can be a great deal, here are nine things to check before you buy, along with some suggestions for where to find a bargain.

It’s fair to wonder whether a used iPhone is as good and reliable as a new model. The answer is: it depends on where you buy the iPhone. If you buy from an established, reputable and well-educated source, think Apple and phone companies, you can assume that a refurbished iPhone is a good iPhone. Be more skeptical of less reputable sellers.

Starting with the iPhone 5, all models work on all carrier networks. It's worth noting, however, that AT&T's network uses an additional LTE signal that the others don't, which can mean faster service in some areas. If you buy an iPhone designed for Verizon and bring it to AT&T, you may not have access to that additional LTE signal. Ask the seller for the model number of the iPhone (it'll be something like A1633 or A1688) and verify that it's compatible with your carrier.

If you’re buying a used iPhone, you don’t want to buy a stolen phone. Apple prevents stolen iPhones from being activated by new users with the Activation Lock feature, which is enabled when Find My iPhone is turned on. But you won’t know if a phone is Activation Locked until after you buy it, when you can’t unlock your iCloud-locked iPhone.