Hmmmm... I'm not sure where you found that grammatical mistakes can cost you a match. The first time I decided to judge a match, the key factors that were laid out to me-- and Shane himself told me this, btw:

-Story

-Trash talk

-Character development

-Relevance

That's basically the four main factors to keep in mind when writing RPs. Some people may actually use very bad grammar and spelling for trash talk, pointing out flaws in the way a character speaks. But, you shouldn't let that get to you. Use that to your advantage, maybe call them out and say how they're so devoid of ideas, they have to resort to picking on the way you speak.

And no, you don't have to use that line. I'm only giving you a piece of advice, not strategy.