Compare Permission vs. Interruption Marketing
If you think about how most Realtors market themselves (Transit Ads, Direct Mailers, Newspapers) they are generally not making use of permission marketing. Getting people interested in what you're selling / doing is much harder than making it easy for people that are trying to find a service, to find you.
Let's look at some of the differences, tools and costs between the two forms of Real Estate Marketing.
You can click and drag the map around to see stuff that's out of frame, or click the mindmeister link in the lower right corner and it'll take you to a full screen version.