Even the most seasoned writer makes the occasional grammatical or spelling error. A lack of errors helps to increase trustworthiness, while a lot of spelling mistakes means you can look like an amateur. While you’re at it, make sure you are capitalizing properly and not ending all your sentences with a multitude of ellipses (…). SHOUTING should be avoided, as should writing in all lowercase. An attention to detail shows care and that you respect your readers.
Proofread your work multiple times. If you can, get a fresh set of eyes to look over your work before you publish it to the web. If you can’t do that, set the writing aside for a while and come back to it later; you’ll have an easier time finding mistakes if it’s not fresh in your memory.