It is very simple. At the end of an Email to your List, to be build that much more more credibility in the Product you are promoting you put your personal RECEIPT to show your Subs that you believed enough in the Product that you bought it and use it regularly. Do not use it every email. Maybe 1 in every 5 or so.
Example : You might say something like this in your email swipe...... ." I was so impressed with this Product I ended up Buying it (see proof from receipt below), and use it day in and day out to help my business grow and profit "
Item: Best Email xxxx xxxx
Price: 17.95 USD
P.S. Hopefully you DO buy every product you promote ? If you do not, you really need to.