-Be suspicious of all environmental claims. Don't trust anything unless you have verified them yourself.
-Look out for poor use of scientific facts, especially when listening to politicians: "Reducing carbon emissions will protect the ozone layer", "this technology is sustainable", "emissions can be offset", "the greenhouse effect is not certain" etc. All examples of rubbish that has no basis in fact, even the last one (think about it).
-Look out for buzzwords that put a gloss on reality: "carbon intensity", "sustainable development", "carbon offsets", "clean technology" etc. Another clear sign that something is being covered up.
How do you spot greenwashing? We had a few suggestions over at Planet Green, but Keith at Unsuitablog makes a few more: