I am getting ready to travel to the other side of the country, and when I inserted my SIM card the phone says it is locked to a specific carrier (it didnt specify which one) and that my SIM couls not be used without the phone being unlocked. Very disappointing, especially since they claim in their description to have a thorough QC process.

Works fine, but it came with a bunch of dents on every single corner and a faulty battery. With normal use, it usually depletes in a couple hours, if you turn on wifi, it would probably last an hour or so. The measurement is usually wrong too, I had it deplete at 30%. Another time I had it warn me that I'm at 10% (after having 60% for a while) battery but on the corner it was at 1% and when I tried to charge it, it immediately jumped to 51%...

Also, along with all other unlocked iPhones, it had a loudass camera shutter sound that you couldn't turn off.

I purchased a certified refurbished 32GB iPhone 5S (Silver) for a family member. I was pleasantly surprised by the excellent condition of phone, it was cosmetically flawless. Also the phone was very professionally packaged for shipment, and included a USB charger and Lightning cable (these were 3rd-party non-Apple accessories, but they worked fine). We transferred the SIM card over from an older phone that was being retired, and the phone activated on the carrier network (AT&T in this case) with no problem. The only issue I ran into was that after a week or two of use, it became clear that the battery in the phone was worn/defective; the phone had trouble holding a charge for a full day, and would sometimes die when the battery percentage still showed 20-30%. So I ended up returning the unit for a full refund under the 30-day return policy, and ordering a second unit. The second phone was in similarly excellent condition, and the battery is working as expected.

Overall I would say that going with a certified refurbished iPhone is a great value, you can get a phone that is just a couple years old, but is in excellent condition, and costs roughly 1/3 or less of the original price. I think a key is to take advantage of the Amazon 30-day return policy, which most of the third-party sellers here seem to honor (make sure you confirm this before you order). Inspect the phone carefully when you receive it, and make sure you test the battery thoroughly over a couple days to make sure it is in good condition. If either is not satisfactory, return it for a full refund within 30 days (which includes free return shipping), and simply order another unit.

After loosing my phone again I needed a relatively cheap option and I didn't really care if it is used or not or how old or new it would be. I only cared if it worked and was cheap enough so that I would not regret loosing it or breaking again. I firmly believe that once you go to apple you never go back, so there was no question about the brand of the phone I was going to get. I really like how user friendly apple is and how well acquainted I am to it, just makes things easier. So I started looking for a cheap option on amazon. Another thing I really cared about was that the iPhone should have been unlocked, coz I was not planning on buying a sim card of any kind, but rather using my phone with wifi. Having these things in mind I knew that I most probably will not find the best possible option, it is almost impossible to find completely unlocked phones. Whatsoever, I ordered this one after having asked if it is unlocked to not and receiving a positive response. In short, the phone was not unlocked, but thankfully it only took few minutes to unlock it with my friend's sim card. There were no scratches on the phone (almost none). Works pretty well and I have been using it for over half year. So far no complaints, will update if I find any.
Overall I am greatly satisfied with the phone though it doesn't perfectly fit the description.

Update: I took the phone to the at&t for the purpose of buying a sim card. The girl who was trying to insert the card, couldn't close it afterwards and she broke that spot(meaning it is not broken, but doesn't fully close/go in). She took no responsibility whatsoever at all on her part, which was pretty annoying, but later on I took it to the apple store. they told me that this happened most probably (but not certainly) because it was a refurbished phone and that it will cost me about 40$ to get it fixed. But since I changed my mind about buying a sim card I did not go for fixing it.

WORST EXPERIENCE EVER WITH AMAZON. If I could give a zero star rating that is what I would give because this phone, an iphone 5S, worked for about 8 months and that was it. One of the microchips was defective. Not worth repairing. $300 in the rubbish. HOW DARE YOU DO THIS TO THE PUBLIC????