Once you've written your presell content, read over it. Have other people read over it. Is it a sales pitch? If so, start over. Is it valuable, useful information that recommends a product or service? Does it tell the reader how that product or service can help them with a particular problem or situation that the topic of your writing covers? If so, then you have written information that will effectively presell the product or service.
Writing presell content takes practice - especially for those who excel in writing sales pitches. It may take several tries before you are able to write good, effective preselling content, but with practice you will get there. Make sure that the people who are reading over your presell content understand what you are trying to do - otherwise, their input won't be very valuable to you. Keep the general rule in mind: Sales pitches are for selling, recommendations are for preselling.
People are turned off by sales pitches. We've even become numb to them, because we hear them so often. Preselling, however, works because it’s a softer sell. The reader feels that you are looking after their best interest by offering information and making a recommendation.
If you have done your preselling right, when the potential customer clicks through to the merchant site, they no longer need to be sold. They already have their wallets open, and they are ready to make a purchase of the product that you worked hard to presell to them.