Amazon has a problem with counterfeit products across the board, not just batteries.

I haven't had to buy any for a while so I don't have a place I can currently recommend, but check out the vaping subreddits, or forums. A lot of vape mods use 18650 batteries, and consequently the forums and subs devoted to vaping are really good resources for finding retailers that sell legit high quality batteries, the ones to avoid, battery safety info, and stuff like tutorials on when and how to re-wrap them if the plastic jacket gets damaged.