Check the Warranty
It’s also smart to check the warranty status of your iPhone. That’s because even refurbished iPhones come with a warranty. If the warranty has expired, it pretty much indicates that the iPhone was bought more than a year ago. It’s always smart to buy a device with some warranty coverage remaining.
You can check the warranty by going to Settings > General > About. Grab the serial number of the device. Then, go to this Apple website and paste or type the number in. The website will give you the warranty status of the device — including whether or not it has expired.