Once a client completes the purchase of an item on your Facebook store, he/she can be automatically redirected back from PayPal to your Facebook store. Here is how you set this up:
1. Log into your PayPal account and click on the 'Profile' sub tab under My Account.
2. Click the 'Website Paymen' Preferences' link under 'Selling Preferences'.
3. Click the On the radio button to enable 'Auto Return'.