I think you should just explain to your friend that you are very sorry but it's really expensive to buy and ship to the Philippines and isn't practical. (Don't even mention the issue of payment). I suspect they'd leave you to pay anyway, and you'd never receive the money. People from poorer places often do this, hoping you'll just send it as a gift. You may not be a wealthy person, but to people in poorer economies, everyone here looks as if they have money, when it's not always true. And it seems as if we have easy access to all sorts of goods, so it's tempting to try to use you.
That's not to say that this isn't a good friend. It just seems like an easy solution to his wanting some organic barley. But if you think about it, many people in the Phillippines must be eating locally grown barley without destroying their health.