How has working a commission only (phone/network of friends) sales job worked out for you?

I am thinking of hiring people to work online for my startup but want your general input on what your experiences have been working commission only. Would I be wasting my time trying to hire someone under this arrangement? What mistakes should I avoid? I worry about losing money if I hire people who don't know what they're doing on an hourly wage.

What's the best way of proving that someone is actually good at sales?

Any feedback is appreciated.