Last year our company wanted to make a large push in Amazon so we explored many listing/inventory management services out there. We tried a few clunkers and only wish we found SureDone sooner. They have the "5 Tools" that make them and their customers so successful.
1. Excellent Customer Service 2. Affordability 3. Online Marketplace Knowledge (Specifically, Amazon + eBay) 4. Easy-To-Use Platform + Great UI 5. Superior Developers
In the past, I've spent way too much money and time on services like Mercent and Channel Advisors. Give these guys a shot, you won't be sorry!