San Marzano tomatoes have quite the reputation. They’re said to be sweeter, pulpier, and less acidic than other canned plum tomatoes, which is why so many people seek them out for their sauces. Unfortunately, most “San Marzano” tomatoes you’ll find in American grocery stores are frauds.
Source: LifeHacker – How to Tell if Those San Marzano Tomatoes Are the Real Deal