All used phones sold online have risks. Search these forums, there's one purchased on swappa that got turned off by Verizon for non payment by original owner, 8 months after purchase. Swappa and PayPal said to late. There will be some that say that's rare, it may be, but it happens.
In this case, note 8 and it comes up as s8, run the opposite direction. If it's not a huge savings, go into your carrier store and just buy one, comes with warranty, used ones don't if your on Verizon. I know for a fact, the year warranty for phones is for original purchaser, been down that road already.