Hey, wall of text incoming!

I have worked at a cell phone repair shop and we sold refurbished phones all the time. The odd one would have an issue, but the majority of the time, there was never a problem. Of course, we were extremely picky on what we sold and would send ones that didn't get through our inspections/QA back to the supplier all the time. It was pretty rare that we sold ones that came in off the street. As long as you are picky about what you get you should be okay.

Best Buy doesn't sell refurbished phones. Those are "Marketplace" sellers and aren't regulated by Best Buy. The sellers pay to be put on the website, similar to Amazon private sellers. Walmart does this too now.

Best Buy does run an auction website similar to eBay, 2ndturn, that they use to sell returned items. This includes phones that have been traded in when upgrading/signing phone contracts. You can get killer deals on Best Buy items here if you know how to play the auction game; games, tvs, computers, phones, etc. This is where a lot of the marketplace sellers get their phones from (and local resellers), they then resell them on the Best Buy website. Source: I worked at Best Buy and people would ask about the Marketplace stuff all the time. Best Buy has no return policy and very limited control over the marketplace sellers. You're taking your own risk by buying from them. Some are good, some are bad.

If you do buy a refurbished phone, run the IMEI through one of the many checks. This can be done on any of the telecom websites; Telus, Bell, Freedom, etc. It will indicate if the device is going to work on their network. If it says it won't, then the device is blacklisted in North America and has been reported stolen. It will work outside of NA, though. The status can show that all is good, and then be blacklisted after you have used the phone for a month or more. Although, I only saw this with phones that were bought on Kijiji (common scam was to purchase insurance when getting a new phone, sell it on Kijiji, and then report it stolen. Phone gets replaced and the seller pockets the money. Buyer get screwed over). Check the battery. On iPhone, there's a battery life indicator inside the settings. On Android, there's apps to download that will indicate the battery life remaining. Test everything on the phone; ports, cameras, speakers, etc. Samsung has a testing function. Go to the keypad to make a phone call and type *#0*#. You can go through and test everything there (except battery life).