How to sell shop items and keep stock right

Pick the item, size and colour and confirm; the sale goes on the guest's bill and takes one off the shelf.

Open Shop and pick the item, and the size and colour for stocked items.
The screen shows how many are left. Confirm the sale to add it to the guest's bill.

Selling below zero is allowed with a warning. Voiding the line, or changing quantity or size, puts the stock back.