Can you clarify? Who's "we"? In many places in the world we still very much negotiate for better prices, and I'd imagine the answer is going to be heavily dependent on the culture you've got in mind.

There were a few American department stores which claimed they were the "first" to institutionalize a one price policy on their items. Wanamaker's was noted as having a one price policy in the 1870s by a few economic Historians, however Hutzler's in Baltimore had a one price policy by the late 1860s as noted by the Maryland historical society. Because of this they claim Hutzler's was the first one price store in the United States and I have not seen anything to counter this argument as of yet.

I think technically an advertised price is an offer to barter ( under English law anyway).It is an 'invitation to treat' - see Pharmaceutical Society of GB v Boots Cash Chemists (Southern) Ltd ( 1953).

No one is bound to accept the price and the contract is only formed when the customer offers money to the shopkeeper and the shopkeeper accepts the offer.

People are able to barter but I think 1) they don't realise the position under law 2) natural reserve.

I have a work friend who barters for everything in high street stores in the UK and is nearly always successful. I hate going to the shops with him because I find it excruciating!