Painting income on the side. How to advertise these services?

I was recently talking to a freind and found out that on weekends and his days off he has been doing painting jobs for word of mouth customers and making the equivalent of 1/3 of his total income from this. The interesting thing is that he now only uses word of mouth but when he started classified ads in local papers and online classified were his main advertising mediums. This shows the advertising power you can achieve through these advertising medium.