I'll go a bit further with this... Much of the time you can't tell the difference on the surface or by visual inspection... it's only when you actually use one that you ultimately find out. This is one of the main reasons to purchase from a known good vendor such as GotVapes that does take the time to source their products only from authorized distributors or direct from the factory itself.
As for what is good or bad... as long as you are purchasing from a good vendor, you have a leg up... then that just leaves which product works well for your style of vaping and your own other preferences. You may not always get a product you like the way it works, but it is unlikely that you get a bad one and if so, the vendor will usually stand behind it and make it right for you.
