Look at the places where people still haggle over crap like a bag of rice or a pair of pants. Their economies are always underdeveloped with a low standard of living. Moreover, look at the most successful retailers: Walmart, Amazon, Target, that Swedish furniture chain, etc. They all have posted prices. They dominate global retail. If haggling was efficient and productive then some Egyptian or Bangladeshi retail chains would dominate global retail. This is not the case. The price tag was one of the most important innovations of capitalism. So why the fuck do we still by cars like some old lady in a 3rd world market haggling over some melons?
Walmart and other big chains offer rock bottom prices compared to smaller operations by amortizing losses over a broad range of products and geography. Lose money or make very little on this product; make a large margin on something else.
That said, I prefer not to haggle over the price of goods. But that said, other models like the sort-of-but-not-really crowd funding model of Gustin are intriguing.