Steve,
I don't specifically go out and do demo's on either domestic or commercial, unless I am already doing something else for them.
I have in the past done a few where I've been cleaning their carpet and they have asked about upholstery or leather and I've given a quick demo of what it might come up like. Always ended up with the job to do either then or at a later date.
IMO once someone has asked for a demo they are literally committed to getting it cleaned fully, otherwise they are left with a lovely clean patch on their suite that stands out like a sore thumb!!