||When you make your living as a writer, you're selling many things:
your vision, your ideas, your energy and enthusiasm and expertise. Also essential to your ongoing success is your eye for detail. "Quality control" matters.
It matters for several reasons. If you are not a stickler for accuracy -- is your profile subject John Smith or Jon Smythe? -- in everything from spelling and grammar to statistics, people's exact titles and quotes, the content of your writing itself immediately becomes suspect. Sources won't talk to you again. Editors won't trust you. Readers won't believe you. Any error can spell disaster: from prompting a libel suit to the retractions made necessary by the recipe suggesting a potentially poisonous ingredient (an error Gourmet magazine made a few years back.)
It's too easy to rely only on your computer's spell-check or grammar police, but it's up to you to read and re-read your own copy. It's also important, whenever possible, to make sure you read the edited galleys of your magazine work well before it goes to the printer. I didn't get the chance to do this with a new client, a national magazine, and found to my horror they had chopped out an entire section of my 2000-word story. This meant the piece was unclear and read badly in the final third, and omitted the first reference to a major source, leaving him unidentified.
I have no problem with being edited -- but I do with a piece that makes my reporting look sloppy. Not only am I now embarrassed to send this piece to my source, who was helpful in the extreme, but reluctant to include it in my clips or my portfolio. The problem could have been avoided if I'd seen the galleys. Insist on it (nicely.)
Sources will sometimes ask to see what you have written, but seasoned writers rarely let them do so. If the magazine you write for has fact-checkers, you can safely assume your facts will indeed be checked and quotes read back to your sources.
If you are writing for a newspaper, though, it's your job, and your job alone, to make sure every aspect of your story is accurate before you submit it.
Don't assume, even as a beginning writer, that it's OK to make mistakes. It's not.