Email marketing

I have had people from Asia, Australia and South America buy, and of course people from the US. But last week, I payed 30 dollars for search marketing, and not a single buyer (at the time I opened up search to every continent). Which continents should I disable and why? By the way they pay with all the main credit cards, so also, which continents have Visa, Mastercard, Discover, and American Express in regularity

Thanks!