The language is always a giveaway. Don't ever do an individual sale thru the mail unless you are ok with losing the payment or the merch.
The language is off for a reason. If you pick up on the language, you are probably too educated to fall for it and are not their target and they've lost nothing, other than a small amount of time, by sending you the email. Their targets are the people who do not pick up on the off language. There was a pretty good chapter about that in ethe sequel to Freakonomics, Think Like a Freak. The audiobooks are make for great listening if you spend a bit of time in your car.
https://www.businessinsider.com/why-nigerian-scam-emails-are-obvious-2014-5
http://mentalfloss.com/article/82814/secretly-smart-reason-scam-emails-are-poorly-written