This reasoning has been used so many times and while it makes sense on the surface, if you think about it for a little longer, then you'd realize it's probably not true. For example, in this case, the bad grammar persisted even in the final stage where the money was about to be transferred. I don't think you really need to "filter" more people at that point.

I'm guessing there was a study of some kind and not just theoretical debate? In a way I would agree with you, but I can also see an argument for the contrary. As in you don't want to change the pattern at this point as that might fire some alarms and spook the horses.

Why Do Nigerian Scammers Say They are From Nigeria? (Cormac Herley, 2012)

https://www.microsoft.com/en-us/research/publication/why-do-...