I've never done it before, and someone suggested just posting an ad on Craigslist and hiring someone, paying them 20% commission.
Does anyone have experience doing this? What worked for you? What didn't?
Commission should be as high as you can, up to %70 is not unheard of. That's because the sales person makes money from the first payment, but after that, the advertiser is all yours to keep. Make sure to get all the contact information within the company from the salesperson and communicate your intent to them.
We have a full-time Director of Sales who comes from a background of non-advertising sales (he worked for a UK hardware distributor previously), and he is by far the most talented salesman ("salesman" makes him sound like someone who goes round knocking on doors, but I can't think of a better word), and there's no way we would have ended up in a better situation if he wasn't with us.
Obviously it depends on your situation, but I'd certainly suggest that there are many scenarios in which paying a high wage for someone who's really good at what they do will bring in more than they cost.