Earlier quoted context omitted.
Which is exactly why they should be banned to keep the market overall healthy. Preventing deceptive practices in a market economy this is a prime example of useful government "intervention", just like supporting contract enforcement or preventing theft
They can always justify it as not knowing the price. The sales tax rate is different in different places. It costs a different amount to ship to Florida than Alaska and picking it up at the factory is free (even if nobody does). The advertised price is if you have your own modem, renting one from the cable company is more. None of these are inherently wrong. You should be paying more if you're having it shipped to a…
There is no reason you can't show final price including tax on the label in a physical shop. There is no reason why a restaurant should be able to charge a 20% service charge instead of increasing regular prices by 20%. If you are buying a concert ticket or airline ticket the displayed price should include all mandatory fees. They can upsell you on additional services, but they can't suddenly notice in the last checkout step that your price is higher because the website you are using is charging a fee; that fee was known to them at the beginning of the transaction and should have to be disclosed at that point in time at the latest. If you want to go even further you can also dictate that shipping and handling fees are only allowed to include reasonable costs of actual shipping and handling.
All of these are normal common-sense regulations in most first-world countries.