3 years ago, we migrated from manually processing eBay orders, to having Volo handle all our eBay orders and inventory management. That year we turned over £320,000. We now turn over in excess of £1.2m with the help of Volo running all our back end processes seamlessly. A truly cross platform system that can synchronise stock between eBay and Amazon, and any other channels such as websites. It is expensive, but when you calculate time saved by using automation, and the ability to sell across several channels. It is worth every penny and don't forget that the price includes a great support package which can be hard to come by with other solutions out there.
They also hold several free business classes and conferences throughout the year which can be really helpful. Your sales are tied to their commission so they really do want you to do well and it shows by their enthusiasm to help your business expand in to as many channels as possible.