I agree with above comments. My view is that affiliates need to optimize their chance for a sale by stacking the deck in their favor.
People buy what they Want not necessarily what they need. Buying is an emotional process. Many merchants just provide the tech specs about the product with no emotion. So testimonials really help and coupons or anything else that helps the customer feel "comfortable" buying or "safe" for buying or "smart" for buying or "look good" for buying helps to stack the deck in your favor. (Notice these are all feelings.)
Study up with some Tony Robbins or Dennis Waitley tapes for some great psychology of selling info.
Another emotional pre-sell is to help the customer "see or feel" themselves with the new product. "Imagine" yourself up in the mountains in your new SUV. Picture yourself in front of the fireplace on a cold winter night in this soft, warm fleece robe from XYZ merchant. I'm being a little corny but you get the "picture!"
I created some short little text links for a client using these concepts. "Travel in Style with Luggage from XYZ" "Travel 1st Class with Luggage from XYZ". These subtely conjure up the image of how good you will look and feel with new luggage for your trip - Instead of the standard - buy now, lowest prices text link.
Read some back issues of
http://www.grokdotcom.com for some great info on increasing conversion rates.