Editing Red light

'''Red light''' means '''do not buy'''.  It is presumably
what you see when you [[swipe the barcode]] of a product
whose [[price premium]] plus its [[retail price]] is not
cheap enough to make you buy it.

It assumes that some [[price]] and [[price premium]] data
have been compared, and that there is another option that
is better that can be substituted.

Or, more likely, a total [[boycott]] of that coded product.
In this case, it means '''do not buy at any price'''.  But at
the [[point of purchase]] no one can see that this product is
''always'' generating red lights everywhere, and for everyone.

A [[yellow light]] is a less strict and more common way to
signal a problem with purchasing a given product, or a price
at which one should buy it (but not for a higher price).  
A [[green light]] just means "buy", and like the red can be
"at any price".  [[KitKat McFlurry]] for instance is red only.

== How to know when to let the red light glow ==