No matter how well you write, or even if you have a professional writer create your web site copy, you're going to have errors. Misspelled words, awkward sentences, phrases that don't make sense, and words that are used incorrectly run rampant through many sites. And it's no wonder. Writing well is hard work. Even a good writer will be too close to the copy and won't see ALL their mistakes, even when re-reading the copy carefully.
Mistakes in your copy can sink your web site. The online audience who accounts for most of your customers are a rather literate group of people. Studies show a large percentage have a good knowledge of spelling and punctuation. If they find your copy has several errors in it, prospects will figure you do sloppy work.
The solution is simple. Get a proof reader to carefully check your copy. You can enlist the help of a friend who has a sharp eye for spelling and punctuation. Better yet, get a professional proof reader to read your copy. Proof reading is almost always affordable and the investment will pay off big time in avoided embarrassment and missed sales.
Don't get too comfortable with spell checkers. Many have limited numbers of words they recognize, and will skip past some misspelled words. One of the most common problems is that a spell checker can't help you if you use the WRONG word.
Don't feel like I'm picking on you. I worked in the TV and movie industries for many years. I can tell you from personal experience that even Hollywood's writers struggle with typos and other errors in their copy. None would dream of turning in a script without first having a capable proof reader go through their drafts and revisions.