That being said, I was EXTREMELY skeptical when I read the OP's post. 15 calls in one day?? I don't care if your ad says "happy ending with your FREE lawn mowing", I don't see how you would get 15 calls in the first day with a Joe Blow hubby and wife after-work lawn service.
You're not very likely to reach that level of customer response. 5 years ago, Craigslist wasn't very competitive. And a lot of people that lost their jobs are now trying to do lawn care, so that creates much more competition. Another factor would be homeowners not having as much disposable income, due to the economic crisis, to hire a lawn company.
In my experience, it doesn't really seem to matter how "good" your ad is. It's all about how you can spam and overpost with as many accounts as you can. I don't do this, because it's wrong and pathetic, but 9/10 ads in my area (Wash D.C.) are from the same person. Most ads are like "Call Jose 555-555-5445 I do gud werk".
Check this out: every single post from the same person. NOT STAGED AT ALL