Just for October Prime Day, Amazon has activated a 35% off coupon that works on thousands of items in its Resale store - Amazon's official outlet for used products. This includes some ridiculously good discounts on newish generation Apple Watches. I'd recommend you get one in "Like New" condition; there's a good chance the unit you receive is brand new and there is only minor damage to the packaging. Resale items get the same 30-day return policy like any Amazon purchase.
The 35% off coupon is reserved for Amazon Prime members only. If you don't want to commit to an annual subscription, you can just sign up for a single month for $15.