There are numerous features within the software that tie to a users facebook accounts.

Highlights of facebook specific features:

• Allow a user to register into your site using their facebook account (Social Connect Addon)
• Allow a user to log into your site using their facebook account (Social Connect Addon)
• Allow sellers "like" their listings on their facebook account from within their client side account admin tool (Sharing Addon)
• Allow sellers/general users to "like" a listing on their facebook accounts from any listing details page (Sharing Addon)
• Allow sellers/general users to "share" a listing on their facebook accounts from any listings details page through the "share popup" (Sharing Addon)

You can find more specifics about the Social Connect addon here within the support wiki

You can find out more about the Social Connect addon with that addons support wiki page here

You can install and enable both the Social Connect and Sharing addons within the following admin tool:

ADDONS > MANAGE ADDONS

Doing so would create the following sections in the admin tool:

ADDONS > SOCIAL CONNECT

ADDONS > SHARING

The only configuration for the social connect addon is to fill in the necessary information provided by facebook within the following admin tool page:

ADDONS > SOCIAL CONNECT > SETTINGS

The steps to setup facebook's login feature is here in the support wiki.

Within the following admin tool you would set which social media sites to you wish to allow your users to share listings to:

ADDONS > SHARING > SETTINGS

One of which is facebook

1. Facebook does most of the heavy lifting with respect to social connect (registration/login) so there is little from the GeoCore side to debug an issue. Our first suggestion would be to go through your setup of facebook app id's and such with a fine tooth comb to find any issues before you start looking other places.
2. Our software suggests to facebook what to place within a like or share using the "og property" meta tags within the source of the listing details page. If you have this feature on you'll see those tags within each page's source code. Note that these are just suggestions to facebook. Facebook can choose to use them or something else in the page. You can find out more through the following facebook faq
3. Our software does a "like" for the buttons the sharing addon places in the my account sharing page and the facebook button in the listing details page (not the facebook link provided in the header.tpl template of the default design).
4. Our software can "share" a listing using the "sharing popup" within the listing details page. Next to the other specific like buttons created for each social media site you'll see a default sharing icon. If you roll over that icon you'll see a popup with sharing links to various social sites including facebook.
5. Users can alternatively paste the url of the listing into a status update or comment on facebook to share as well
6. Like's may or may not create a story in a user's timeline.
7. You can also use the facebook debugger found https://developers.facebook.com/tools/debug and insert your url to see if there is something you can do to make sharing/liking more reliable to your expectations.