It annoys me when ordering oil and your quoted a price per ltr and they accept your order..... that it is usally 0.5 or 1.00 cent per litre more when you get the bill. They should be obliged to stick to the quoted price or inform the customer that it may cost more on delivery.
I even saw on back of receipt from one supplier that the price on the day may not be the price on delivery. Thats fine if delivery is not for a week or two.
Surely they are able to keep an account of there own stock levels in order to cover the quoted rates to customers.