Need to Enhance 450 Listings for Amazon, eBay and Google

We are seeking a strong eCommerce candidate who has specialization in optimizing product listings. We have more than 450 product listings of our products that we sell on Amazon, eBay and Google. These are products used in medical industry. We have a great brand and sell through these channels along with our website. However we notice that when customers search for keywords our products don’t always rank high on Amazon even though we are cheaper than most of our competitors. We are the original manufacturer and we notice that distributors of foreign competitive products even though they are more expensive end up getting listed higher. I need someone to help solution this problem for me and help us rank our products higher on Amazon, eBay and Google. Amazon is the highest selling platform for us, so I am fine if we first start there. This will be an ongoing relationship under a NDA and Non-Compete. We will leverage you to do work for us for different clients in eCommerce. You must understand what it will take to rank higher on these platforms. Please answer the following questions in your response: 1) Have you done any such work before ? 2) What do you think are leading causes of products not listing high on Amazon, eBay and Google? 3) What will be your solution approach to address the business problem? 4) How quickly can we address this for all our listings and what is the effort you are proposing this needs ? 5) Will you guarantee your work or it will be best effort basis? Thanks