Yes, the free shipping is the clincher. The GIA cert checks out. Of course that doesnt mean they have the stone that matches the cert, only that there is a stone that matches the cert. Wouldn't such a stone be famous already?
Odd though that the proportions of the stone pictured on ebay L/W is .7090 and the L/W of the dimensions in the cert is.6694. Though when I measure the other pic on ebay it comes up .711