The latest upgrade to Flint‘s mobile payments app looks to leverage both sides of the merchant/customer transaction.

The new iPhone app allows merchants to set up pre-set lists to make inputting transactions faster and more efficient. Customizable receipts make it possible to search and organize customers based on transaction details like product type and card used. These features potentially provide additional marketing tools, allowing, for example, targeted loyalty offers to selected receipts.

The new app also sports Facebook integration so customers to directly post ratings and reviews. For the those businesses that have avoided social marketing due to time limitations or integration concerns, Flint’s app makes it easier to get the customer to do some of the work.

More than 20,000 users have downloaded Flint since it was first available late last year, opting for the dongle-free approach to taking payments on the go. The average transaction has been more than $100.

Watch Flint’s most recent demo from FinovateSpring 2012 here.