It is not a scam, it is an attempt to reduce traffic and pollution making urban areas safer for residents, tourists, historic buildings and works of art. Most Italian settlements operate these zones and way, way more fines go to Italians than tourists.
Had you done a small amount of research about the driving laws in another country before you went there, you would have very quickly found out all about these zones. There is clear signage and I am afraid you will have passed both a warning sign and then the international driving sign for limited vehicular access.
Sorry to sound harsh, but you have been a bit daft for driving somewhere without checking what the road laws are and then having been rightly ticketed for breaking the law, you make accusations about scams and attempts to rip off tourists.
I know it is galling to receive an unexpected fine like this, but the sensible attitude to it is to take it as a lesson in life about checking up on basic road rules before driving in a foreign country.