When registering a client, in the program for accounting for goods in a shops, it is possible to assign him some kind of club card. This can be helpful in increasing customer loyalty. Then you can easily find the client you need using his card number during the sale. We indicate the client's club card when registering, here in this field:
Now he can be found on this map in the search menu. Figuratively speaking, it is like a barcode on a product.