I'm going to go with the great wine fraud

Chiropractic medicine

capitalism

ITT: Things people personally think are scammy, but not actual legally-defined scams.

Windows

Capitalism

HR departments in corporate jobs.

Lottery's the expected value is always lower than the prize of a ticket. And even if you win it is on the back of other poor desparete people who lost. An then there is the fact winning often leads to a lot of other problems.

Neither are scams but the UK is fond of permanently doing temporary things. Income tax in the UK was first imposed as a temporary measure to fund the Napoleonic Wars but after Waterloo it was never repealed since it brought in so much. Same sort of deal for the 70 mph national speed limit, it was a temporary measure in the 1960s apparently in response to someone caning it down the motorway in an AC Cobra and as we know, there’s nothing more permanent than a temporary solution.

Enron, perhaps. I think it qualifies.

A good documentary: https://en.wikipedia.org/wiki/Enron:_The_Smartest_Guys_in_the_Room

Phoebus Cartel, essentially the few oligopolistic light bulb companies got together and colluded and intentionally reduced the lifespan of light bulbs.

Battle Passes

But in history it took forever for people in Holland to realize that Tulips are not worth entire plots of land

Neoliberalism!

The second is financialization.

Both are huge scams still running.

1950 to present antipsychotics whose severe side effects are written off as crazy talk.

The Bernie Madoff investment scandal. Started in the 1970’s and continued into the 2000’s. It eventually dissolved in 2008 during the financial crisis. There’s a really great documentary on Netflix about it.