Should I buy a certified refurbished iPhone from Walmart?

Refurbished from Wal•Mart means they cleaned a used phone as best as they can.

Such as this one:

https://www.walmart.com/ip/Restored-Apple-iPhone-11-Carrier-Unlocked-64-GB-White-Refurbished/131975201?classType=REGULAR&from=/search

• “Like-new” condition with very light micro-scratches, invisible at a distance of 8-12 inches (arm’s length).

And it's not even being sold by Wal•Mart.

Sold and shipped by Reebelo

There's not much of a way for you to know what you're going to get from Reebelo. Though they do get very high marks for honesty on Trust Pilot.

https://www.trustpilot.com/review/reebelo.com

Seems it would be okay, but it's up to you. And I would very carefully look at each offered item to see where it's from, and that vendor's reputation.

And as Jeff Donald mentioned, it's very unlikely you'll have any warranty coverage.

It’s unlikely anyone from Walmart will respond here. I suppose the advantages are a lower price. the question would be who is warranting the device and if you need service, will the provider use genuine Apple parts and what support they will offer you.