I'd not thought about this particular way of scamming. But you make a good point. When I've sold stuff for lightning in the past, I have usually created an invoice because I've been worried that the buyer might make a mistake (accidentally pay too much). Zeus has a point of sale function in their app that I've used before: it allows you to set up products and just tap the products to add to an order and then bring up the total and it automatically creates an invoice for that. It's pretty slick. (I believe Breez also has a PoS, but I haven't used it yet.)