Indie authors don't always have the funds to hire a professional editor and may rely on their own eyes and software to do the final edits before printing or converting their digital files. As an author and someone who writes every day I can tell you that this is a big mistake! Typos can be found in any work, even those produced by the big publishing houses but when they show up in indie works, they take away from the reputation of the trade. Readers by nature are harder on indies but they also love finding a great novel among the stacks of unknowns so it's important to put well written, polished and professional works out on the market. So, what do you do when you can't afford an editor? It's simple, really. Use the resources that are available to you.
It's amazing how much more adept at grammar, spelling and punctuation the young can be! Probably because they've just had these things hammered into their heads at school. High school and college students can make great editors for these types of errors. They may also provide valuable insight along the way if they are your target market. Maybe your references are outdated or too mature. They will definitely let you know. If you don't have your own child in this age range, borrow one from a friend or relative. I have found some that are happy to do it for simply the promise of a mention in the forward of the book. If you don't mind paying a little for the service, its possible to post a want ad at the local college for an English major to help you out in return for some spending money and work experience.
Other authors also make good editors. If you belong to writing groups, you may find other authors to trade editing services with you. It may not be a good idea to share your unpublished work with an online contact whom you've never met, but if you have someone you trust, they can be a great help.
We hate to burden our friends and family but if you have avid readers in your arsenal they may just love to help you with your edits in exchange for a sneak peak at your work and the writing process. I've found that many readers are fascinated by the writing process and would love an opportunity to be a part of it.
As writers we become emotionally attached to our work and that makes us too close to pick out even some of the most minor errors. We stare at our pages so long we no longer see the individual words because we are looking at the story. For this reason any second set of eyes is better than none. The first time I published an online article I spent hours scanning it for errors. As soon as it was published, I pulled it up and was humiliated when I found a typo in the first paragraph! Don't let this happen when you see your finished book for the first time!