Is your number one service/product the thing that is most important to your customers?
Sometimes what they think is the most valuable isn't the thing that is best for them.  Whether it is or it isn't, you need to make sure that your website conveys this message in a very simple and clear way.

There are a few ways to evaluate what is your number one product, is it:

• your top selling product (or range)
• your most profitable product
• the product with the most value to your customer
• the most desirable product

Take a good look at your statistics from your sales and also from your website, are you sure that you have understood your customers adequately?
Is your best product featuring adequately on your homepage?  Perhaps the best product for engaging your customers is your way in to talk to them about your other services or products?