This is a question that I get lots. Why are people not buying? There could be lots of reasons why and it is important that you take the take to work it out. Here is a few things worth checking out.
The buy button does not work - Yes you heard me. Lots of times people leave their site running for weeks and even months before actually checking if the checkout process actually works. Get a friend or even try buying yourself and ensure the whole process actually works. It fact make sure you get a friend to check it out in case you are logged into the systems and so it works for you but nobody else.
You are not addressing their concerns - This is an important one. Think of at least 3-5 reasons why somebody wont buy from you and address those concerns on your sales page. If there is even one reason not to buy, of course they wont.
Pricing is wrong - Are you competitive? Have you checked out the competition? Being more expensive is not an issue if you can demonstrate why. However If you cannot then people will simply pay less for the what they believe to be the same.
Nobody can find you or knows you exist. - It is not a case of build it and they will come. They wont. People are busy and wont to find the quickest way to solve their need or pain. You need to tell people about your product or service and often. Use all of the available tools and platforms that make sense and where your prospects are.
Nobody wants your product or service - This is very common. You build or create what you think is game changing and everybody will be stumbling over each other to give you their credit card. However without any validation or research you are taking a huge risk.
They have questions that you are not addressing - Every single question about your product or service is a piece of content that needs creating and made easy to find. If they cannot answer their question on your site they may just go and look for the answer elsewhere and end up buying elsewhere as a result.
 They don't trust you or your site -  There could be all kinds of reasons why they don't trust your site but if for any reason they do not feel you will deliver the goods they will simply buy elsewhere.
So there you have it 7 reasons why people may not be buying from you. Always think about the customer and the experience you are providing and get in their shoes. Remember, people do not care about your product or service they care about their needs, pains and problems.
Talk about the problem you solve and then how you do it. Make it easy to buy and ensure you answer their questions and address their objections.
I hope this was useful. And I have no doubt there are hundreds more reasons so please feel free to add to them in the comments.