People buy things on the internet.
There are a lot of ways to buy things on the internet.
The key to getting others to buy online from you is trust and simplicity.
So many people make purchases on Amazon - and not just because of the great selection and prices - but because they trust them.
Use a modern-looking shopping cart interface.
Take a look at the examples below. Which do you think is more likely to get pressed?
If you said the one on the left, you're weird. If you said the one on the right, you'd be with the majority. It's simple, clear, and modern-looking. It helps remove indecisiveness. And if the button changes color slightly when the user's mouse hovers over it - all the better (and more fun to click).
Furthermore, you'll notice newer sites with buttons like the one above on the right. A lot of older sites - you know, the ones with LOTS OF CAPS, random things in bold or tons of colors - telling you to BUY NOW BEFORE YOU MISS OUT - those old eCommerce sites that were plentiful in the early 2000s use the PayPal button above on the left. They often sell outdated products or look like they haven't been touched in years. Which image would you rather be associated with?
It's funny how significant a simple button can make in the bottom-line of your online store, but also don't forget the shopping cart.
In general, make sure the experience is as intuitive as possible. The fewer the steps that the user needs to take and the less information that they need to provide, the more likely that they'll complete the shopping process (as opposed to abandoning their shopping cart - aka closing site after they planned to buy something, but decided to stop in the buying process).
Some Good Tools/Services