it's easy for someone who doesn't do this full time to be able to low ball and not give a care. I can't count the number of single season customers we've lost over the years due to the home owners previous "mow on the side guy" being desperate for money and undercutting us by $10-$15. The way I see it is, let them have it.
If we charge $35 for a 40 minute yard and they want to do it for $20. Fine. I guarantee the other guys won't put in near the effort or quality of work that we did. It comes down to people want something for nothing and they care more about saving a $$$ than the quality of the work.
We made a decision a few years back to start targeting upper-mid level housing and above and people who value quality over a cheap cut. We've never looked back.