Hi Paul,
I have attached a sample document (all customers are fictitious and the transactions are dummy transactions), the following would happen if you sent it to the printer duplex:

First piece of paper would have Aaron on page 1 but on the back (page 2) would be Abington which we would not want as they are sent through the post to customers.

Second piece of paper would have Adams and Company on page 3 and on back (page 4) would be Allen Bros.

Third piece of paper would have Amazon on and on the back would also have Amazon which is fine as both sides are for same customer.

We need it to insert a blank page if the even numbered page is for a different customer to the previous page. The example above would ideally print as:

Page 1 Aaron, page 2 blank, page 3 Abington, page 4 blank, page 5 Adams and Company, page 6 blank, page 7 Allen Bros, page 8 blank, page 9-11 Amazon, page 12 blank.

Hope this helps.

Thanks, Stephen.