Not sure how they taste, but the Oneplus 10 sure looked like a Hershey bar when Zach (Jerryrig) broke it in two.
Two-types or phones.
Trade-in phones. Most likely, they run it through a process of testing and replacing any needed parts and from there depending on the age of the phone, it will be sent to a different global distribution company that places into a country where it can sell the phone.
Once read that India, China, or Russia three of the largest markets for used phones (maybe not Russia this week) however, African, Latin America and South America are also large territories. In that same article it was noted these phones are not necessarily used for reman replacements by the manufacturer since most of the trade ins are for models well out of the standard manufacturer warranty period. But I would guess many are used for insurance replacements but cannot say I read that in the article.
Also, if you visit the Samsung site today, they are selling certified refurbished S21 models and some older NOTE models. S21 Ultras going for about 1K. Not sure what they were giving in trade ins.
Warranty/policy returned phones.
As for phones returned for warranty reasons, they are checked over, repaired and then used as the remanufactured models used for replacements under warranty. That's why early on for a release, if there are not that many returned, your replacement will be brand new, then as the models come back under warranty or just the standard return policy, they are sent out as replacements under warranty.
That's all from memory of a few articles read over the years.
Found two of those old articles:
https://www.gizmogrind.com/blog/what-happens-phones-that-are-traded-in/
https://www.businessinsider.com/what-happens-to-your-old-phone-2016-2