And then there's dark pools. Trading isn't even done on the market anymore.
This is such a non-sequitor, it undermines your entire post.
Food: - restaurants definitely compete with each other, mostly in each local area - and within that, different slices of the restaurant business more directly compete, e.g. fast food is more competing with each other than fine dining. - BUT: we have a huge problem with a lack of competition in the supply chain driving prices up for everyone, at least in the US. - Groceries are similarly impacted by supply chain monopolies
Smartphones: high end smartphones are a oligopoly: - Apple vs Samsung vs HTC and several other tech companies producing phones; Apple definitely commands quite a bit of a premium, as do some of the nicer Android phones. But on the whole, the companies really are fighting to one-up each other with better features, battery life, etc. - quality is improving, even if the price is over-charging vs the ideal competitive market. Low end phones are even more fiercely competitive
Other electronic categories seem to show decent market dynamics; headphones, earbuds, usb peripherals, keyboards, etc. all seem very commoditized; there certainly are brands that try to command a bit of a premium based on reputation / marketing, but the cheap options are often good enough and definitely have a very competitive market. Big electronics like GPUs and gaming consoles though I think it's easier to start considering market distortions due to more monopoly power.
Of course there are no shortage of monopolistic practices out there, e.g. for utilities, collusion on rent, online retail (Amazon), textbook prices, medical care & pharmaceuticals, and even more mundane things like frozen potatoes and chicken.
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The thing that bothers me most with the simplistic view that "the market will do it better" is that the whole premise of market forces giving the most efficient price assumes that (a) a commodity is being traded by (b) a large number of buyers and sellers, none of whom have any significant share of the market. Many markets either (a) aren't trading a commodity (e.g. iPhones and Android phones aren't interchangeable so Apple can command a premium price) or (b) have consolidated buying or selling to the point that they don't have the large number of independent buyers or sellers necessary to have the price be set by market dynamics rather than the monopolist or monopsonist. And the people promoting "let the market fix it" either are too dumb to realize that, or more likely are letting their rich friends make a quick buck or want to score political points by promoting smaller government.
What could be interesting is to have the local government found a co-op, i.e. they issue a bond to do the build-out and then hand the network to a co-op in exchange for a contract to pay the debt, essentially giving the co-op the backing of the government's credit rating for the initial build-out. Then the co-op board gets separately elected by its customers so they're directly accountable to the customers for any shenanigans.
All that to say, voters here do care about utilities, and the coop solution worked for about 25 years iirc but it can't work in today's "one solution fits all" regulatory context anymore, at least where i live. Things are far from that simple in practice.
For trains it's much harder - yes, there are two providers on the WCML, but they're not equal (one runs faster trains) and as such there's zero real competition.
So you have the government own the tracks, contract with a private company to maintain them. Then anyone can use the tracks, like anyone can use the roads. Private companies offer train service to the public. All they need is rolling stock and they can start selling tickets. You then get a market that looks like airlines, i.e. entering the market is a moderate investment (millions; buy rolling stock/planes) rather than needing billions to build the network itself. More popular routes get more suppliers, which turns into more frequent service. There is plenty of competition because rolling stock is mobile and can easily be reassigned according to customer demand.