Is Self-Editing ever a Good Idea?

One of my biggest frustrations involves the perception on the part of authors that professional editing is only an option. Typically, upon inquiring whether an author has had their work professionally edited and I hear, almost inevitably, "I've edited it myself" or "I have spell check" or "My partner/spouse/child/neighbour/co-worker looked it over".

Self-Editing
The inescapable truth is that, as authors, we are NOT able to judge whether we have successfully conveyed our ideas, because we already know what we want to say.
Very few authors are trained to spot verb-tense inconsistencies, awkward phrases, style inconsistencies or even simple grammar.

That being said, there are some tricks to revising your manuscript that you can do yourself:
a. reading it aloud, to yourself or to someone else
b. reading it backwards to catch spelling and grammatical mistakes
c. computer grammar and spell-check, as a starting point (although this should never be exclusively relied upon)
These should never be used to replace a professional edit, but can be used to revise the manuscript before an editor sees it.

Spell Check on the Computer
This should never be relied upon as the sole source of vetting your manuscript, for a number of reasons:
a. These are dialect specific, so as a Canadian, my spelling will differ from both American and British versions.
b. Most computers have spell-check but not necessarily a check for grammar. Homonyms frequently escape this detection (eg. foul and fowl)
c. highly technical or unique jargon is problematic
Again, these do not stand in the place of a thorough, professional edit. 

Non Professional Editing
While a professional edit is expensive, there is really no substitute. Often I will try to help writers find a reasonable facsimile where the price is out of reach by suggesting they find a graduate student or teacher. Sometimes this works out well, but sometimes, writers will substitute someone who is not trained to identify these issues. While I think it's great that your partner/spouse/co-worker/neighbour wants to be supportive and give you their input, their qualifications are not necessarily up to snuff.

In short, is any other form of editing able to replace a professional edit? My answer is a resounding NO. Who wants to read a book full of typos and syntax erros? A professional edit is ultimately a sales tool.

If you can't afford a professional edit, you aren't ready to publish.