You can set messages to automatically leave positive feedback for your eBay auctions. Once you've connected your eBay store, you can set this up in the Store Information.
Head to your Account Settings (the wrench icon in the upper right).
Next, select Selling Channels and then Store Setup from the sidebar on the left.
Once there, click Edit for your eBay store.
Here, scroll down to the bottom where you can input three messages that will be randomly chosen for each of your auctions.
Make sure that you Save your changes. The feedback will be given when the label for your auctions is created.