How to Convert Visitors into Buying Customers?

Help is need it! I have a site for an affiliate product (main landing page + Wordpress Blog). My traffic is by now, about 150 unique visitors per day. Approximately 20 of them are visiting the buying page, but for some reason they do not complete the sale. I have no authority to change anything on that page. I have made some fake buying attempts and realized that the vendor of the affiliate product gets the data and start sending emails to the potential customers (my potential customers). How can I overcome this? What else can I do to convert the potential customers?

• I have my landing page optimized following some very helpful instructions from other BHW members. I have doubled my potential customers from about 10 to 20 already (still not converting)
• I have a discount offer (the lowest price I am aloud to give for the certain product)

Shall I try to add an auto responder in between the buying page by giving away for example a special tutorial guide, or something else? Maybe move the coupon code away from the landing page and after the potential customer fills his email, to send it then as a bonus?
Any suggestion is appreciated. Thank you.

1.Use Landing Pages
2.Analyze Google Analytics
3.Offer Valuable Content