I am beginning to write for profit and I am seeking thoughts on what makes a good short story.

A good short story has elements which leave the reader thinking about the story for a longer time than which they read it.

http://jerz.setonhill.edu/writing/creative1/shortstory/ is a really good overview on short stories and the elements of one.

In general, having a meaningful conflict in the context of your character's the most important thing IMO though, whether it be with themselves, others, etc.

Be concise. This doesn't necessarily mean your writing has to be dry and lack description (I'd actually rather see purple prose in a short story than a novel, since it's over quick). This means you need to make every sentence, sometimes even every word count. Even if it doesn't move the story forward, make it interesting. Creative description, word play, varied sentence structure. You don't want any fluff in a short story. You don't want it in anything but a report with a page requirement really, but it's especially vital to make everything matter when you only have ten (or however many) pages to say it.

Write your story. Read through it. Read every sentence out loud, and ask yourself "Is this needed?" "Can I rephrase this?"

six. Lots and lots of six.

Lots of mystery usually. Since you don't have time to explain as much in a larger novel.

Wrap it up with a nice little twist or better yet fridge horror.

It's really great if your protagonist has a conflict that at first seems to be with another person, but ends up being with him or herself in actuality. I find that a personal conflict (man vs. self) tends to produce a much more intimate story that resonates with a broader audience.