[abhinav061]

Scammers intentionally make grammatical mistakes. If you can spot the mistakes, they don't want to engage with you.

(Of course, there are other reasons why would one spot yet ignore grammatical mistakes - sometimes it is because of the personal situation they are in, sometimes it's of empathy towards non-native English speakers)

[imiric]

Most scammers aren't that smart. The grammatical mistakes just happen to work well for them as a filter.

[_vertigo]

I’ve heard this a lot, but is it actually true?

[goto11]

Unlikely. I believe it started as a hypothesis to explain the many spelling errors in scam mails, but I don't think this have ever been confirmed to be intentional.

Hanlons Razor is probably appropriate here.