The amount of current a battery can deliver also varies. Flashlight forums where people sometimes want the maximum power output will point you to a couple of specific 18650 parts and a similarly small number of sources where you can be reasonably sure they aren't counterfeits.

(Some) manufacturers provide specs for their batteries, but most of them are coming from no-name factories in China with no reputation at stake, so there's either nothing published or it's exaggerated.