One of the common ways that Realtors will get links on the internet is by reciprocal linking. This means that you see another site and you both decide to add a link to each other, this is a little like blogrolls on some blogs that you see today. The idea behind reciprocal linking is that when you add a link to your site and another site links back to you that google will like you both better as you have another link pointing to your own site.
That is not quite right though.
The reason that Google likes incoming links to your site is that gives your site authority status, people should trust your site because others trust you enough to add a link to your page. If you give a link to another site Google looks at this as you giving authority to another site so they would cancel out. But this is still not quite right because if this was the case then you should never link to another site and then everyone linking back to you will give you a number one ranking in Google but this is not actually the case because Google does still like links, if you give out none then Google will not really trust you.
So now this idea of linking to and from other sites comes down to trust. There are very complex algorithyms at the Googleplex where the Googlers try to make sure the results at the top of the search engine are the best results. To do this there are a lot of factors that Google looks at. The best thing for you to do though is to not try to trick the system with reciprocal or other links but instead to look at the content that your readers would be most interested in and giving that to them. At the same time make sure that you are using the social networking sites like Digg, Reddit, stumbleupon, Activerain and others to make sure that your site is at least getting noticed and if your content is good enough then you deserve anyway to be an authority, which is what you were trying to be in the first place.