International markets vary wildly. Some countries are very price sensitive, while others demand features. You have to tailor your marketing for each one.
-Price. Your $399 piece of software might sell well in first world countries like the US, but in developing economies like India, you probably have thousands of customers looking for something $99 to free due to the difference in market rates there.
-Payment. Even in the age of technology, payment through internet or electronic transfer is difficult. Each country has a different system of banking that can cause numerous issues. This forces customers and vendors to go through third party services adding an additional layer of cost. Very undesirable.
-Support. Customers still like to be able to pick up a phone and reach you when they are having difficulties getting your gadget to work. Problem is, your 2pm might be 2am for an international customer. Unless you have 24 hours international support, they might look closer to home.
-Awareness. Sure adwords and google work well for getting customers to your site, but not all countries have high internet connectivity. In some places printed media still rules. Find ways of getting an ad into a local publication or newspaper.
The best way to solve many of these problems is to start a channel sales program. Search for and develop relationships with overseas vendors who do business in these overseas markets. Work out contracts with them for pricing tailored to their location. They will be able to handle all the marketing and support a lot better than you in their own area. Just make sure they know the product inside and out.