Careful:batteries at 80% potentially.
Potentially worse than 80 percent. I had three Apple Watch refurbs from woot under 80 percent. Plenty of others had the same issue.
Is the only recourse in those situations to return the product or accept a low value adjustment? Is there opportunity to use the battery replacement option and Woot cover the cost?
I’ve never heard of that happening to anyone who posts on the forums. I sincerely doubt woot would pay the $100 to have a battery replaced.
They accepted all three of my returns but it was a hassle. And disappointing.
Thanks for the reply and personal experience share.
If you want really robust battery health, class A refurbished or factory certified refurbished (by Apple) is the way to go. 
(My 13 Mini “class a refurbished “ came with 90% battery health, and a few more dings than promised. But the screen was nearly perfect so I kept it.)
The first watch I purchased from Woot (Series 5) was advertised as Grade A Refurbished with a minimum battery health of 85%. It arrived with only 79%.
Unfortunately, the refurbished grades on Woot (and probably many other sites) are WILDLY inconsistent.
I think your suggestion to get Apple factory refurbished is the only surefire way to be assured of useable battery life.