At the recent RWA conference a panel of 2 reputable agents and an editor held an "American Idol" workshop in which someone read the first 2 pages of a manuscript. The panel would say 'stop' when they felt they'd reached the rejection point. For many, it was obvious that the writing didn't hold up. However, in others, it seemed arbitrary. The fact that they said they hardly ever looked at the query letter but went straight to the pages seemed unfair, as they would reject something set outside the US, for example, as soon as a location was mentioned. However, stories often begin with an 'elsewhere' incident, and the action could move to their good old US of A on page 3, which they wouldn't get to if one of their reject countries was mentioned in paragraph 2.
One way around this might be to call that incident a prologue, in which case one would hope they'd read on if the writing was strong enough, but then we hear that prologues aren't in favor, especially when the action picks up only a short time afterward.
Since the panel was requesting partials from a few who made it through two pages without being cut off, I'd think they weren't being arbitrary. It's enlightening to see what kind of slush you wade through daily. But it's scary to think that agents will toss your stuff without even the slightest interest in the 'whole' picture and decide they know where the book is going based on three paragraphs. Are we that predictable?
What's a poor novice to do? If my writing sucks, or my story doesn't interest you based on a query, so be it. But what if my chances are shot to heck because I set an opening action scene in another country, or mention a dog (yes, KY, some agents say they auto-reject dogs)? We don't have a master list of what not to do for each agent's pet peeves.
This is exactly why the phrase "query widely" appears regularly in Miss Snark's pearls of wisdom. This is why you do NOT make a list of three "dream agents" and get all pouty when they say no, or worse, get pouty if they pass it along to an assistant or colleague who DOES like it.
There is no checklist. There is no master list. All you can do is query everyone you can and write as well as you can. Some queries are going to be rejected for arbitrary (foreign lands) and/or stupid (no dogs) reasons.
I can see this is frustrating as hell to writers, but honest to dog, there isn't a short cut around it. Don't be tempted by anyone who tells you there is. Usually that shortcut come attached to an invoice amount and a lot of hype.