As with all moral or ethical paths, living an ethical life becomes a greater and greater balancing act between subtler and subtler distinctions as you travel further. The choice between a Fairtrade and non-Fairtrade item is easy; the choice between a Fairtrade and an organic product is harder. I do not believe the human mind can encompass all possibilities, so there might never be an equation to answer these questions for all circumstances; however, access to more information will aid consumers in choosing one of the better of several ethical options.
For some further information on why these dilemmas matter, I have added an article I wrote on climate change to the Miscellany.
Melting the Candle from Both Ends (Davetopia)