In the online world of market-spaces and places your product description is going to have a huge impact on your success rate. Considering that people want to know and understand what they are purchasing they will inherently scour these descriptions for information. Without being able to inspect the products before purchase they will rely on whatever information is present and therefore writing a strong description is necessary.
Clear and concise make sense here. Be specific in the beginning and let them scroll down for lengthy descriptions. Attention span is short in the online world and having the most common questions answered quickly will improve conversion rates.
Provide diagrams, pictures, and other displays that might help them visualize the product. While market-spaces like Amazon only allow the first picture with a white background it is beneficial to include pictures of the product in action. These pictures make impressions and motivations.
The word usage should be active and encourage a purchase. Don't be too vague as it may seem like you are offering a solid product. People who are searching for information to make a purchase might be looking for sizes, specifications, and other information so they don't have to return the item. It will help you in the long run.