Writing classified ads can be broken down into 4 rather simple steps, "Attention," "Interest," "Desire," and "Action." AIDA is a well-proven formula that all types of advertising can benefit from. It is designed to grab the readers attention, get them interested in what you are trying to sell, make them desire what you are advertising, and then get the reader to take the action necessary for getting more information. It is important when you want your ad to have a good conversion rate to make is easy for readers to see exactly what you are providing and why they should want it.

This is my summary for http://www.websitemarketingplan.com/Arts/WritingClassified.htm

While I agree with what he says about the structure of an ad (common method actually, used by many marketers), I can't say the same for his copy. It's not bad... just not real great. I wouldn't recommend looking off of his copy on there for writing your own (at least for online use). From what I have gathered, the style of his copy would do better offline rather than online.