[AnimalMuppet]

I wouldn't use a study. I'd ask about their own negative experiences - where a contractor did something, and it took them another six months to fix it. If that's ever happened to them, they'll get the point without needing a study.

[insoluble]

This approach may be suitable with more experienced clients, but smaller/newer clients may lack the experience or "self-awareness" to reflect in this manner.

It's curious that inexperienced developers are bad for clients while inexperienced clients are bad for developers. Perhaps it takes experience to appreciate experience. At the same time, inexperienced developers may go well with inexperienced clients since they can learn together -- albeit with plenty of inefficiency.