I'm a writer, so grammar is extremely important to me. Bad grammar says so much about the person. Like my mother always said, "You can buy things and you can even buy people, but you can't buy class."
Internet marketing is all about selling yourself. If you don't even care enough about yourself to speak your native language properly, what does that say to people you want to trust you? We've all seen promotions full of ESL with poor spelling and English composition that is like nails on a chalkboard when you read it. These are always the people who want to know what they are doing wrong and why no one is buying their products.
My suggestion is that if you can't speak proper English (or whatever language you are selling in), hire someone to do your writing for you and to edit your videos before you put them out there. Not that we're trying to sell to the hoi poloi here, but I would be ashamed to send out some of the stuff I've seen.