There is a little more to it than people answering this thread are telling you.
But to hopefully point you in the right direction a little on Amazon.com:
Amazon Best Seller Rank 50,000 to 100,000 - selling close to 1 book a day.
Amazon Best Seller Rank 10,000 to 50,000 - selling 5 to 15 books a day.
Amazon Best Seller Rank 5,500 to 10,000 - selling 15 to 25 books a day.
Amazon Best Seller Rank 3,000 to 5,500 - selling25 to 70 books a day.
Amazon Best Seller Rank 1,500 to 3,000 - selling70 to 100 books a day.
Amazon Best Seller Rank 750 to 1,500 - selling 100 to 120 books a day.
Amazon Best Seller Rank 500 to 750 - selling120 to 175 books a day.
Amazon Best Seller Rank 350 to 500 - selling175 to 250 books a day.
Amazon Best Seller Rank 200 to 350 - selling 250 to 500 books a day.
Amazon Best Seller Rank 35 to 200 -selling500 to 2,000 books a day.
Amazon Best Seller Rank 20 to 35 - selling 2,000 to 3,000 books a day.
Amazon Best Seller Rank of 5 to 20 - selling3,000 to 4,000 books a day.
Amazon Best Seller Rank of 1 to 5 - selling4,000+ books a day.
Look at the books that are the best sellers in your niche and decide if you can create a book that is going to be of the same or better quality than them. If you cannot do that, you should think twice about producing a book that is of inferior quality to your competitors and expecting good sales.