It starts by the mechanic not minding being duped, so long as there is money in it for him. We mechanics all subscribe to magazines written for the professional mechanic or shop owner. In these magazines are articles of all sorts. I have read many useful and informative articles in these magazines. And the manufacturers of these machines pay the magazine many thousands of dollars for these full-page ads.
Modern gasoline has additives in it to prevent carbon buildup.
Yes, but it seldom does. But Honda, Ford, Toyota, GM etc. By the way, while we're on the subject, I do happen to have a different machine in my shop that cost me lots of money. What this machine does is cleans the air in your car's tires. Here's how it works, we hook the machine up to each tire, then the machine removes the old, stale, dirty, used-up air from your tires.