It's completely up to you! On one hand, there is the risk that you're buying a used device without any warranty, which can be nerve-wracking. However, on the other hand, you may be able to get some warranty protection in place if the device was bought new. So, it really all comes down to your individual situation.
Remember: always research any potential purchases – second-hand or not – before making a decision. Never buy anything online without first checking to see if the seller has a positive rating and/or a warranty in place.