If you're sending traffic to sites as an affiliate, watch out for sites that include an ordering telephone number on the home page.
Easily 50% of your sales could be lost by people that will phone instead of shop online.
In such a situation one must always remember that many people are still not convinced of online shopping, especially people aged say, 35+. So be especially wary on sites that those people might shop at, e.g. bookstore, classical music etc.