On every invoice for orders from our online store, I put a note giving the customer number and asking the customer to put that customer number in the store's order message field on any future orders.
To date, about 3 people have actually done that.
What happens too often is, one time a customer gives his name as Michael and the next time as Mike, and I wind up setting up the same person with two different customer numbers.
So PLEASE - if you get an invoice, READ THE NOTE and note down your customer number. In future this number will also be used for Return Authorizations. It's YOUR unique Airgun Designs customer number!