Here’s one. When folks either misuse a word entirely (“effect” for “affect” for but one of many examples) or spell words phonetically (or nearly), it’s a pretty good sign that their literacy skills are pretty thin.
For example, I saw “amuck” used by someone whose verbal vocabulary exceeds his literacy. The word he was groping for, of course, was “amok.” (It’s a fascinating word.) I’m willing to give folks credit for trying, but I’d really rather folks used words they actually KNOW (as a result of good literacy) than spout off with words they really don’t know at all.
Actually, I’d be more charitable had the fellow typed, “amuk,” since that’s an early 17th Century variant spelling. Both spellings derived, of course, from “amuco.”
Oh, and yes I do know that some contemporary folks are arguing for “amuck,” but that’s really just because they’re too lazy to learn how to spell and use words well.