Flying one of the programmes mentioned it briefly, I think they said there had been five such cases in Canada (no time scale as far as I recall) and cited relationship breakdown between commissioning parents. Not something I had thought about either. Baby being damaged goods for whatever reason would be the most likely cause to spring to my mind.
I really recommend listening to his programmes which are available on bbc iplayer for a long time yet, sorry I can't post a link, for some reason, perhaps because they are podcasts, it doesn't have a "share" button, you have to find it for yourselves, use search work "surrogacy".
It has done nothing to change my mind regarding the acceptability but I definitely feel more educated on the subject and they were well presented and an enjoyable listen notwithstanding the subject matter.