1. Include links to samples. If you don't show samples people doubt your ability and the quality of your offer.
2. If you are selling resale or plr always include the high quality avi version... chances are if you are like 99% of the people producing online you do not have the knowledge or the right tools to encode your videos to satisfy all your clients.
Many people will want to encode the video themselves to change the dimensions, reduce the file size, reduce the bit rate, and improve the image quality by using the best encoding tools on the market... by providing the avi versions you do not have to guess for them.
Why not make your self more sales? Take these tips to heart and you will.