I have been placing the receipts in the box with their orders. I am now considering, to stop this and just only add a thank you note card (4 x 6) in the packages instead. If you look at many vendors and/or businesses; they do not include invoices because the customers have the invoice sent to them after their purchase. And many buyers on Etsy are members or have an account, therefore, they can download this if there is any issues with their order. I'm trying to cut cost down with paper and printer ink as well as be environmentally friendly. As with shipping I will no longer be offering the guaranteed shipping. Cost are going up everywhere including materials, shipping containers, paper, etc. To me, cutting out the paper invoices is not only cutting down cost, it is also becoming more economically friendly and aware as I would feel the customers can relate to that as well.