The eternal question of a writer trying to get published, right?
The thing is, it’s so hard to tell. I doubt there’s any way to really answer that question. Perhaps if one knew an editor (publishing company, magazine, etc.)… Interviews, such as D.L. Snell’s, might give some clues, but even that is based on how the editor was feeling on that particular day.
I’ve been reading and listening to stories in more of the professional publications lately, and sometimes it’s hard to tell why those stories got accepted and mine didn’t. Now, some of the stories there are blow-away, and that’s obviously why they were picked. But others… not as much. And I’ve read stories that blew me away in smaller publications, too. “Junk Drawer” in the previous issue of Allegory (the issue before the one in which “The Widow and the Stranger” appeared) had me thinking about it for days. Some stories I’ve read at EDF have amazed me, too. So the professional publications don’t corner the market on the best fiction. Far from it!
In the end, I guess reading is just too subjective to quantify. And if my reading is that subjective, editors’ reading must be as well. My first writing prof (taught undergrad fiction writing) said that publishing was 10% the work of writing a finely crafted story and 90% the luck of getting that story on the right editor’s desk at the right time (i.e., when they were in the right mood for the story to appeal to them). I don’t remember the exact percentages, but it was something quite lopsided like that.
Of course, reading the stories or books published by a market will give you some insight into what the editors want. But the stories can vary so wildly in quality, style, subject, etc., that it really seems to become more of a crapshoot.
I suppose there is no secret to this (though if you’ve found it, please share in the comments!). The best thing to do is to focus on honing one’s craft and making each story the best it can possibly be, then sifting through the multitude of markets out there and submitting repeatedly until you find one that sticks.