Thats a policy to have when buying things in general. Even more so when gram for gram it holds 1% the energy of gasoline... but doesn't need the help of oxygen, or any decernable trigger to make a hash of things.
A common practice by shady sellers with 18650 lithium cells is to advertise a group of 4 of them as "2000mAh", but it's the total of each cell, not the individual cell ratings. So you're really getting four 500mAh batteries, which really sucks.