Some people 

I’m just finishing up with one of those clients who buys your service, but it transpires has no awareness of IT at all. Queue screenshots, videos, phone calls, documentation, repeating the same information several times over…

I pride myself on my patience, and being able to explain technical jargon in useful terms.
But when someone struggles to even use fullstops in their own correspondence, well, that should be a sign to stay away.