B&H is very reputable. And I'm pretty sure they have a decent return policy, but you should confirm.
Half my gear over the years has been purchased used -- from online stores as well as direct eBay purchases. I've never had a significant problem. (Years ago, bought a 20 year old nifty fifty for $50... And a couple years later, the aperture blades became sticky -- only time I ever had an issue).
Remember, unlike most consumer electronics, lenses are meant to last many many years. Some scratches on the body don't affect performance.