Twenty years ago a fast food company had exactly this problem. Groups protested about the dominance of the restaurant chain and pointed to some dubious practices in South America that allegedly was resulting in the deforestation of large areas of rainforest to produce grazing land for the beef stock. Now in 2013 this particular company appears to be very responsible with the sourcing of its products, the way the food is cooked and their transparency about the nutritional values in their food and drink.
Obviously when a company does get large it requires the services of suppliers, transporters and other agencies to support it in delivering to its customers. No doubt there is trust between the company and these suppliers. When this trust has been ignored then this is where the problems start.
The large company has a public face, the suppliers don't. It is therefore the large company that takes the flak, the public anger, the criticism. Ok, may be they should make more stringent checks. But what is a world without trust?