The frustrating thing is that I know this, but because the voice in my head is my voice and has my accent, "of" and "have" sound basically the same so when I'm speed typing I accidentally write "of" and when I'm proof reading it, either out loud or in my head, it sounds the exact same to read "could of" or "could have".

I've gotten around this in my professional writing by proof reading everything out loud while doing a silly accent. Or getting a screen reader to read it back in a robot voice.

But for random comments on the internet, I don't bother, so I'll occasionally get a helpful person explaining the mistake, and they're always polite and I appreciate it. I just wish I knew how to make it stick when I'm actually writing.