Social Store doesn't post your items to your wall, instead it creates a store tab for them in your Facebook page just like here:
If you want your items to be automatically posted to your wall when you list them, you can set that up through your eBay account, just follow these steps:
1. Go to My eBay, you will find a link to it at the top of any eBay page.
2. In your My eBay page click on the “Account” tab.
3. Next in the left side menu choose “site preferences”.
4. Under “Selling Preferences” > “Share your eBay items with friends” choose “Show”.
5. Click on “Facebook”. Next a Facebook login page will open.
6. Once you login you will be shown this message asking you to authorize allowing access to “eBay selling feed”, click on “ok”.
7. Next, you will be asked to authorize sharing your items on your news feed, click on “confirm”.
8. Once you get this message you will know that you successfully linked your eBay account with your Facebook profile. Now when you list items they will be automatically posted to your news feed.