One of the drawbacks of using the “Google Cash Method” of direct linking to a merchant’s sales page is that Google Adwords only allows one affiliate/merchant ad to be displayed per destination url. What this means in effect, is that if another affiliate or the merchant himself has outbid you, then your ad will not show if you’re linking to the same sales page.
In order to advoid building landing pages to send Adwords traffic to, some affiliates will perform a redirect to the sales page from their own domain. However, this is against Google’s terms of service and if they find out, will disapprove such ads.