We've used Shipwire on and off for a couple of years and have generally been happy. Getting set up we had a few bumps in the road, but a lot of that was on us.
Overall we've had a great experience and have had very good customer service. Been impressed with their willingness to work with us on some features we required that were a bit out of the ordinary.
Currently we use a few different fulfillment services state-side and are in the process of testing them, but Shipwire has been our most consistent vendor over the years, The reason for 4 stars: pricing could be a bit better.