Do companies who market themselves with ethically labelled products do what they say on the tin? How fair is Fairtrade?

Any advice / experience / opinions on this would be warmly received, as the whole subject of "eco-labelling" and "corporate greenwashing" has become a bit of a minefield for many consumers, and corporates alike. Especially in the case of individual products attaining green accreditation, but the companies that produce the products don't necessarily need to adhere to it on a corporate level.