Becoming a reseller is all about the network that you have in place. If you are able to get in touch with a wide range of clients that have a need of your services, then you will be able to purchase a varied inventory from the experts that design content your clients need. Your prophets as a reseller will come from being able to connect those clients with the content you purchase from designers.
Cost management is an important part of being a reseller. Develop a strategy for paying the designers of content that will help you prepare the materials your clients need in a timely manner. Once you have started building a network of clients that pay you for your services, you will be able to set a rate for your materials that is greater than what you pay designers.