That's a tricky one to ascertain though. The proposed model where they have to engage with a number of professionals and, perhaps more importantly, spend money ensuring all is in order for a sale may be as good as you can get, but even that's a long way from certainty.
I don't think agents who are paid commission on the sale are best placed to make such a judgement. It's not that long ago I was sale agreed on a property, surveys and all complete only for one of a number of siblings involved to change their mind at the last minute. The agent was pretty annoyed, certainly didn't see that coming.