Lots of good advice here. No, I would not say anything to this guy - just be on guard but not paranoid. $20 sounds like a good deal to have the lawn mowed. I am surprised that realtors don't let you know though, I assumed in this current day that they either would or would be *required* to let you know. I personally check http://www.familywatchdog.us/ from time to time for my own area and for the areas where my kids live. We also use concealed carry as was suggested - not for everyone but it is our right and is a good one.