<?php
$og_type = 'article';
$og_url = $this->product->product_url;
$og_image = JRoute::_('
http://www.yoursite.com/'.$this->product->images[0]->file_url);
$og_desc = $this->product->product_s_desc;
$og_title = $this->product->product_name;
$doc = JFactory::getDocument();
$doc->setMetaData( 'og:type', $og_type );
$doc->setMetaData( 'og:url', $og_url );
$doc->setMetaData( 'og:image', $og_image );
$doc->setMetaData( 'og:description', $og_desc );
$doc->setMetaData( 'og:title', $og_title );
?>
Insert this code in the product details page template in the beggining to have a nice open graph tags for Facebook.