> I struggle to believe that most scammers in the world are that good that make deliberate mistakes in their letters to reduce false positive rate. More realistic solution is that the average scammer is not well educated, he makes mistakes unintentionally and out of pure luck it works well for him.

These people are doing it as their actual job.

The scammers are not kids who are having fun with a prank, or hobbyists who make mistakes because they do not spend enough time on the task. The scammers are smart human beings who do their jobs, as professionally as they can.

If they wanted a foolproof version of their text, they would be able to find an automated correction tool (e.g. on Gmail), or to ask someone to proof-read it. The fact that they do not is a hint that it is either a waste of time from their perspective, or detrimental to the efficiency of their jobs.