You've really only covered two points - why corporate customers won't RTFW and why they ask for discounts. If you are dealing with a corporation you might get contacted multiple times through multiple channels, but probably not from the same person in a short period of time.

Disrespectful and abrupt communications are still a warning sign for larger companies as are unrealistic expectations (at least for the example given).

The article specifically mentions that "Any one of these warning signs is not a big deal, but stack 2 or 3 on top of each other and (depending on their severity) you have yourself a red flag." A corporation might only set off 1 or 2, and if you keep in mind the points you made I don't think it will generate too many false positives.