As a mw, like the pp, I don't expect callbacks from those who've decided not to hire me. In fact, when we interview I always say--'think it over, talk to other mws, whatever you need to do to make this decision. I'll know if you call me again, that you decided to hire me'. Most who choose elsewhere do not call back and that is fine with me. Occasionally someone does call or email to say 'no thanks'--and they use the kind of simple and courteous/friendly messages that were mentioned here already. Once as a client interviewing mws, I did go so far as to name 'issues' I had with one mw w/whom we'd actually done a couple of prenatals, actually-so it seemed more important to do this when we changed our minds. Besides, the woman really bugged me! She ended up telling other mws in the community that I was 'dangerous' ! but it didn't impact our ability to get the mw we wanted in the end. With the others, I just dropped a quick note thanking them for their time and saying that we'd found 'the perfect match'.