I think its best, as a rule of thumb...to simply not buy from unknown random internet sellers on ebay, amazon, etc....as the reviews are fake almost 100% of the time on battery sales...and the small percentage of honest dealers are too hard to tell from the mass of fakers.
After that, don't buy anything ending in the word "fire" unless the only prefix is "sure".
Essentially, you personally cannot buy a Panasonic 18650 FROM Panasonic (Same for Sony, etc). They only sell surplus laptop and Tesla, etc, production, to mass producers of after market/private label cells.
NONE come protected. The after market reseller adds the protection, the over wrap, etc.
ALL the cells you see are made by some major manufacturer, sold to a reseller, and, relabeled.
The PROBLEM is that in China for example, there is no enforcement, and, clones/knock offs are normal, not the exception.
No one actually has rights to the name "Ultrafire". There is no "Real" Ultrafire. You can buy Ultra fire wraps, and make your OWN Ultrafire cells. (There ARE companies fighting to own it...no one has won yet..)
Part of the above problem is anyone can rip open used laptops, take the used 18650 out of them, put on a wrapper and/or even a fake PCB...and put anything on the label they want...its just ink.
The 18650 might have started its life as a 2600 mAh cell...and be about a 1000 mAh cell now....no problem, put a new wrapper on it, and sell it on ebay as a Suretocatchfire 10,000 MAH super high capacity Protected Cell.
Unless you have a way to test it, you may not know its both dangerous AND over rated.
Some don't even HAVE an OLD 18650 in it...some had a few OLD AAA inside, some had flour, etc....its a total crap shoot.
Another clue is the rating itself...and the price. If you think about it, why would a high capacity state of the art cell, that had protection added to it, sell for less than the cell it was supposed to be built from?
The Panasonics for example came in distinct mAh varieties, based upon their chemistry.
The most common were 2600, 2900, 3100, 3400 and lately, 3600. If a rating is IN BETWEEN those, say 3000, its fake. If its over 3400, its fake (They're not going yo use real 3600's). Even a rated 3400 is probably fake. (IMR and other cells have their own mAh break points though)
The chargers are probably either fake, or, so poorly soldered and thinly wired that they're a fire/explosion waiting to happen. Add fake protected cells to fake protected chargers, and you might as well have bought fireworks.
So, this is why its important to buy from trusted dealers...parties that don't accept fake stuff.
Don't trust the fake online reviews of the products, or the sellers...fake reviewing is a full time job in China for example. Its in their want ads.
If trusted people in this forum are OK with a vendor, they are probably OK. Even they can be hoodwinked by a bad apple in their supply chain...but the odds are way way down at least.
No one with a good reputation should sell you an Ultrafire though, ever.