The first thing I would do is take a look at the landing page that visitors are clicking through to. Is there anything on the page that you feel would distract or deter them from ordering on that first visit? An 800 number for example, or is the price too high?
Try to view it from a visitors perspective, starting with the keywords they typed into the search engine when they found your page in the listings. You can generally find these in your site stats through your control panel. Click through to your page, compare the article/content to the keyword(s) you used, look at your call-to-action for the affiliate program. Is there any way you can match their interests better, or pre-sell the product even more?