I went to a talk on "local foods, local medicines" on Saturday, by my
herbalist friend Basil, which talked about how different climates produce different kinds of foods (at different seasons). Basil was suggesting that the constitutions of the people, and the environment around them, meant that the local foods were most suited for them. He talked about foods being heating and cooling (i.e. a salad is cooling, and salad foods grow during summer, and in hot summer. A veg stew, however, is warming, and root veg grows during winter/cold climates).
He also pointed out that the fashion for exotic fruit meant that by the time the fruit actually ended up being eaten, it had lost most of its nutrients, and was essentially just a blob of water, fibre and sugar. (Many fruits are picked under-ripe, and then kept inert until reaching their destination - they are then 'gas ripened'.)
The absolute best way of consuming local fruits and vegetables, he suggested was to grow our own. The difference between a store-bought tomato from spain, and a tomato picked and eaten within the hour was huge.
He then said the same thing applies to herbs and medicines. The craze for echinacea (for example) in the treatment for colds, has meant entire countries being denuded of the stuff. In actuality, some of the most effective treatments for colds include yarrow, elderflower and peppermint - all things that grow in England and are very common. He also pointed out that, in many third world countries, the herbs are picked by untrained people doing it just to make some extra money. Because some herbs can look so similar, the chances of getting something different is quite high, and once it's been chopped and dried (and made into capsules, in some cases) it's impossible to tell. Many of these are then sold commercially as supplements or alternative medicines.
With a local supplier, on the other hand, you can assess their knowledge and qualifications directly - or, you can pick your own, which means you are the only one responsible for your training and care.