Looks like it was half written.

But, step #1 is pull up it's spec sheet and replicate their capacity testing method. At least for single cells. For packs there's not much you can do but buy from trusted places- manufacturer, bhphoto (for cameras).

18650batterystore has always been good to me, at least for the 300 Samsung 25R's I bought.

yea they note nothing can be verified visually but one option is to verify the part/mfg #,

“For most of these products, they are sold with part numbers that show an equivalency to a manufacturer’s part number."

Doubt i'd do that, would probably just source from name brands.

"One test, called a destructive physical analysis, involved dismantling small cylindrical batteries. This immediately revealed differences in quality."