How to determine effectively whether my paper is in scope Given the title and the abstract of a yet-to-be-published paper, I asked the PC (co-)chairs of several A/A* conferences whether my paper would be in the scope of the corresponding conferences. Surprisingly, I got an unconditional "yes" answer each time, even for really far fetches for which DBLP showed nothing close in the past years. I suspect that the PC chairs wish to lower the conferences' acceptance rates by welcoming my paper and having the reviewers rejecting it quickly for some formal reasons unrelated to the content (since the content wouldn't be that interesting to the reviewers).

Officially, the scope is formulated very broadly for each of the conferences.

Now, what's the right way to get an objective opinion about whether my paper is in the real scope (vs. an official one)?  I'm working completely alone without helpful colleagues to ask.
I don't know of PC chairs who would deliberately "game" the acceptance rate for a conference, especially an important conference. On the other hand, they do want a lot of submissions. Often they want to build a variety of viewpoints and research into the program, so your "outlier" may actually be a good thing to them. A lot of submissions makes the reviewing more tedious, of course, but allows the program committee to build a more inclusive and "interesting" program. 

Of course the reviewers will give detailed feedback to the chairs and the conference program committee so the answer you got isn't indicative that you are more or less like to have the paper accepted. 

Some conferences have very narrow scope, of course, and I suspect that the answer from the PC would be different if your abstract didn't sound relevant to them. 

I suspect that you already have the best advice you are likely to get. 

The only caveat I have here is that if the conference is so gigantic that the PC can't really respond to such questions they just have boilerplate answers to all conferences. But usually, someone would take a look at it. Committees are generally big enough that someone will look.