Decent spelling helps sell more of your stuff. Notice I did not say Grammar. You need to match your words with your audience. It is OK to not be grammatically correct, although you should try and spell things correctly. People do not talk properly when it comes to grammar.
You want to make sure your brand looks good on Social Media and on the web! ( I usually follow this rule, but not always )
I pretty much am lacking in both and yet the reason how I got around being dyslexic and a bad speller was with tools.
Here are 2 tools that can help you write better sales copy. The first one is Grammarly which is also a pretty darn good spell checker. It has a Firefox extension that allows you to check whatever you are writing online. Social Media, forms, your site, etc. They have a great free version.
The next, one is the Hemingway Editor and it has a free version that works great too. The paid one does not do anything extra by the way other that you can have it on your computer.
It makes sure you are not talking above your audience and can help make your writing easier to understand.
It gives you a readability score that can really help your sales. You want to write your copy at about a 4th-grade or 5th-grade level.
If you use either one of these, let me know what you think!