Or maybe this post would be better titled, What to Do Proofread and, if necessary, hire a copyeditor.
I’ve already been very honest about my shortcomings when it comes to grammar and punctuation so when I come across a query where I can see tons of grammar and punctuation problems I know there are problems.
Your query reflects your manuscript in every way and if its riddled with errors I’m going to be fairly certain your manuscript looks the same. Think of your query as the first page of your manuscript. You wouldn’t send the book out until its shiny and perfect. Your query is no different.