Stop sending them direct to the vendors sales page, instead make a squeeze page related to the product you are promoting telling them they will get a free guide on it or something for opting in.
Collect there emails in getresponse or aweber and setup 7-10 days worth of autoresponders, each day you will email them telling them about how great the product is detailing it's benefits etc and include a hoplink to the sales page until one day they will crack and buy it.
Also you can use the email you collect in future to promote different related products.
Sending people direct to the sales page really is a waste of traffic as you only have one chance that they will buy it there and then, this way you can build a relationship with them at the same time convincing them to buy it and you have 10 chances to sell them.