As an order management and integration software ChannelAdvisor is comfortably the best option currently available. We deal with marketplaces across the world in multiple languages and no other provider has been able to offer the same coverage or speed. The setup was extremely easy and the system is very intuitive with no real IT skills required to be able to use it. With order management, advertising and other services available you can quickly make the system pay for itself with the time you can save.
A slightly wider range of sites would be great but given Channeladvisor already cover more than the competition and are always adding more this is not a major complaint.
The support provided during setup is exemplary and once the system is live the resources made available mean answering most questions becomes very easy. When direct support is needed response times are good and the staff are knowledgeable.
Overall we would highly recommend Channeladvisor as an integration partner for marketplaces and more.