system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When you get a "refurbished like new" phone as a warranty replacement from your carrier, where did it come from and what did they actually do to refurbish it?

I'll give you the tl;dr:

My 3 month old Samsung Galaxy s5 broke and the service representative determined it was a no fault hardware failure. They are sending me a "refurbished like new" phone.

.....I'm wondering....since the S5 has only been out since April, why would they have a reliable supply of refurbished phones already? 

What do they do to refurbish them? Am I going to be getting someone else's problems, or are the refurbished phones just as good as new ones?
gpt
In most jurisdictions, it's illegal to sell a product as 'new' once someone has purchased it and opened the box, even if they immediately returned the product right afterward.

Many of these 'refurbished' phones are just open box purchases that were returned for whatever reason, so they are sold as 'refurbished' at discounted rates even though they are virtually new and unused.

Sometimes refurbished actually involves fixing a damaged or heavily used unit (e.g. by repairing a broken screen or a faulty battery, replacing the outer casing etc.) to bring the device up to a like-new condition.

Items which are certified refurbished usually come with a warranty just like the purchase of a new product and appear to be in new or almost new condition.

The only problem with refurbished items is that there may potentially be a hidden fault (which has not been identified/fixed) that caused the previous owner to return the phone in the first place. So you may be unknowingly getting a phone that already has some sort of hardware problem that's potentially a ticking time-bomb.