I had some 18650s from a head-torch setup i foolishly aquired on DX.com (home of the finest quality, at fantastic prices, that may in fact not be fine quality, but will remain a fantastic price even if the item explodes when you take it out of it's package, removing your fingertips and blinding You..) and although they were a brand i was sure were awesome, as they had the words FIRE and MEGA and COOL on the label, and the spec showed they would pump out 50A at 5v for 3 months 100% duty cycle, they turned out to not function as i had hoped at all. I was sure i was investing $5.46 for 6 of these (inc. shipping) wisely, and the credentials all checked out: Label has a Black background colour, red and yellow flames, picture of a GT-R doing a burnout on box, they were battery shaped, and the Mah was measured in 'Gigawatts per year', but they mysteriously all failed to recharge properly or not hold any charge at all, or in fact be just the label wrapped around a tube of cardboard filled with re-cycled air.
Needless to say, i put my foot through my monitor and sent the bill to DX.com, then went up the road to my local Bricks & mortar shop with my sad story, and they comforted me by doing the LOL NEWB dance/finger point for the required 3 minutes, before selling me a pair of Sonys. I still have them, and i know i don't need to peel the label off to see what they really are, because my local guy has a very big shop window that has been there, totally un-smashed, since he opened.
eBay is the other place i have not been burned on - obv. use people with products that check out when you lurk on torch or vape forums, and people who come up in searches on your local ebay suffix (.ie for me here in Eire) rather then FREE SHIPPING FROM CHINA - as that's that Moderatedfrom dx.com again i assure You.