I can't speak for UK folks, but in the US there are a limited amount of shops where a customer might negotiate a discount. At any brand-name retail store (such as Wal-Mart or Target) the prices are determined by a corporate office and employees have no authority to offer discounts. If, however, you are shopping at a privately owned shop that sells high-end appliances or furniture or jewelry, or at an automobile dealership, you might ask the salesperson "Is that your best price?" or "How much would [this item] cost if I paid you cash right now?". Or you could be coy and hover over a paricular item and when the salesperson asks "May I help you?" you could tell him/her "I really like this [item] but it's a bit out of my price range." Sometimes the salesperson will then begin to negotiate with you and offer a lower price.
If the shop assistant has no authority over the prices and has to tell a customer such, he or she would simply say something like "I'm sorry, but the prices are as marked. I can't offer any discounts."
It's pretty much the same in the UK. You can also ask things like 'What price could you offer me?' as well, but there are not that many shops where we barter- the ones Ouisch names and antiques, second-hand shops, possibly markets, etc. You'll see a lot of things on special offer or promotion, but not much bartering.
If you have a question about the English language and would like to ask one of our many English teachers and language experts, please click the button below to let us know: