You are right, there is much more involved in a painting quote than square footage.

The purpose of getting a quote from a painter is so you can 1) meet the painter and 2) compare his quote with that of other painters. Variables that need to be pinned down so that they are all quoting for the same work include: who is buying the paint, the brand of paint if they are providing it, how many coats of paint they are going to apply, whether the area needs to be primed, and whether they will do prep work such as sanding bumps and repairing holes. And probably others.

What graywings said. And I would add: do they remove light fixtures and replace them along with the switch plates,etc. Do they cover furniture or move it out of the way and move it back.
Painting walls with a lot of cabinet and moulding may seem like you have less square footage therefore less cost, but prep work including masking is of utmost importance IMO and takes time. Some painters charge by the job, depending on what it is, rather than keep to square footage or hours. I have a longtime trusted painter that has done both types of jobs for me and because I know his work ethic and quality, I take his "quote" as fair and honest and don't bother with further quotes. I like to paint as well and do what I feel like doing for myself. But when it comes to the more complex areas, I leave it to "Jack" and pay the price.

I would begin by getting recommendations from neighbors or friends based on quality of workmanship and go from there. If a job is well done, you won't even worry that you may have spent a little extra money.