Never buy a refurbished or used SD card. This not only opens you up to wasting money on a fake or damaged card, but it could also lead to malware that's secretly stored on the device.
SD cards wear out over time just like any type of storage device. If it's refurbished, the life left and storage capacity are significantly reduced and it's likely been damaged in some way.
Learn more about how SD cards work and how they differ from SSDs.