Most true professional sales people won't work for commission only. It's not about confidence of their ability to sell, it's about their value.

You could begin with a guarantee of X dollars for the first 3 months then scale it down over the next 3 quarters to a base salary / commission / bonus / benefits / car allowance package.

Like MNTommy Boy stated, if they generate millions in profitable sales, and you end up paying them $200K, then it's a win for everyone. I would go back a couple jobs ago to check their stated performance as well as their references.

Additionally, you could offer a period of employment of six months and follow that up with long term employment.