You haggle over most things that cost more than $50,000 because those things are unique and their value is subjective.

I don't haggle over the price of gasoline or milk. It's not because the price is low. It's because the identical product is available from a dozen local merchants and I know which is cheapest or which has the best lit parking lot or which has self-checkout. Price becomes so standard that merchants try to compete in other ways. And for those that do choose to compete on price, $0.05 difference on a $5 item is a big gap.