If it’s a expensive/portable item that’s being sold, the risk is there I suppose. Normally if I’m buying computer equipment or a car, I’ll go, check it out first. Then if I want the stuff, I’ll run to the bank and withdraw the cash and/or meet in a public place to do the exchange.
With a contractor, I feel like the risk is minimal, since there’s no guarantee that the person calling the contractor will have cash available right there. They may choose to pay with cash after the job is done, or by check, rendering a robbery attempt useless. A scam like that would result in a lot of wasted time for the robber!
The only time I’ve actually been robbed was 10 years ago outside of Wash DC — got back to my car after paying for gas, and found some kid with a Tec-9 expressing a strong desire to possess the keys. No need for Craigslist.
Keep in mind that you’ve cited 10 examples from around the country. Craigslist traffic is something like a billion ads per year (say 500 million are in the US).