For me, I couldn't think of turning such an important role over to someone else on the indie level with indie money. The question is do you have editing and composing skills, which I believe I do. Today we have access to any music you could need. But you have to spend hours listening for the right combination that tells your story, then blending pieces, slowing it down, speeding it up...etc. This is what a lot of the online composers are doing anyway.
People tell me they can't seperate my score from the story because it has become that integrated. So, until I can afford Speilburg's composers, I would rather do it myself rather than hire it out and, like others have had to do, end up changing it later anyway. But this is just my formula, everyone has to do what they are comfortable with.
I don't know that a LOT of composers online are doing that (you're talking loop/prerecorded music manipulation, right?), though I'll take your word for it. I think anyone aspiring to be a composer is doing just that...writing the notes. And we're trying to learn too, just like the rest of you, to be the next generation of professional composers. Or more specifically, we've chosen the indie-education approach rather than traditional music school, which I'm sure most of you can relate to. I can't speak for everyone, but I know I'm egotistical enough not to want to use material I didn't write, even as much as drum loops. I want drums, then I'm going to play/edit/sequence them myself!
These approaches are not mutually exclusive. I recently worked on Flicker Pictures' recent documentary "Sheryl's Keyosk" -
http://sherylskeyosk.info I provided him with sketches for the music he wanted, and he manipulated (mostly speeding up) the clips to fit what he had in mind. When I did the final drafts, rather than playing it at double-tempo (all the non-orchestral instruments are played live, including a little bit of the harp), I played as originally written, letting him manipulate them as he wanted. After, of course, including the revisions that he wanted. The music became a collaborative effort between me as a composer and him as an editor, which suited the quirky documentary.
Not knocking your approach, of course. As you say, everyone has (and should have) different methods.
Back to harm's question, absolutely can't hurt to ask a composer to work for free. Worst they can say is no. As far as what to look for, even an absolute beginner should have stuff to listen to, even if it wasn't composed for a film. Being able to make great music does not necessarily mean that they can make great music for film, but it's a good start. My first paying gig I was asked to demo a couple scenes, but for a non-paying gig that might be a little overkill.
Make sure you post to the classifieds here on IndieTalk; there are a lot of composers floating around looking to build their portfolio!