'back-end sales' itu penjualan setelah barang pertama terjual.

The absolute best point for a backend offer on any sale is right after the initial sale while the customer still has their credit card out. For example, whenever I go buy a pair of shoes it always seems like once you have the shoes picked out the salesperson will then ask you if you would like laces, polish, etc.

http://www.akamarketing.com/backend-sales.html