eBay's Global Shipping Program is a great way for domestic retailers to ship internationally without a whole bunch of hassle. While the program is fully compatible with ShipStation, you'll probably want to separate out these orders to ensure everything is handled appropriately.
Because each eBay order includes a reference number in the first address line, you can create an automation rule to tag each order and easily distinguish them during your normal order processing.
1. Assign a tag that you want to apply to the orders. If you don't have a tag, you can create one on the Orders tab by going to Tags > Manage Tags.
2. Go to your Account Settings (the wrench icon in the upper right).
3. Select Automation and then Automation Rules from the left-hand sidebar.
4. Click the Create Rule button.
5. Name your rule, and select the "Only apply these actions to orders that match specific criteria" radio button. Then, select the following criteria:
6. Select Add an Action. Choose to Add a Tag... and the tag you've made for GSP.
7. After adding any other actions you want for your eBay Global Shipping orders, Save your changes. Now, whatever actions you specified will automatically apply whenever you import new orders filtered through that tag.