Can a directory of businesses (similar to giveandgetlocal.com) track which online orders were a result of a user coming from their site?
If the directory of businesses site is connected to the sellers account with OAuth and processes the payments through the application then yes. There are fields in the order where you can set the source of an order or a reference_id. Also the payment will have application_details which contains to name of the application that processed the payment. 