A handy MySQL query to check a Magento DB for potential duplicate orders!
SELECT `quote_id`, COUNT(`quote_id`) AS `qty_duplicates`, `increment_id` AS `first_increment_id`, GROUP_CONCAT( `increment_id` SEPARATOR ' | ' ) AS `increment_ids`, `created_at`, `state`, `status`, `customer_firstname`, `customer_lastname`, `customer_email`, `grand_total` FROM `sales_flat_order` GROUP BY `quote_id` HAVING COUNT(`quote_id`) > 1 ORDER BY `created_at` ASC
