I do apologize maybe I wasn't clear enough. In my defense, it was late, and I was typing on a laptops missing a few keys. To clarify the question I would like to say, that the second idea would not include a third party. Here's more info okay.
Users would utilize the site very similar to XStreet SL's old search and listing engine, however with the addition of extra searchable fields and data. Therefore the following would be true:
Users use in-world mechanisims to list to a public website (owned by someone else)
Users would be able to manage their listings in a centeral area along with data and other statistics
The website to which users post will be managed by someone other them.
This is the main idea that I personally feel would work the best, due to the fact we have people like Peggy which manage their own listings on their own websites. This setup would allow users to install a plugin with WordPress and utillize pre-scripted modules in Second Life to post to their own website. Here's a little run down...
Being that this is a plugin, you would own it, you would have your own site, you would be responsible for the listings, not a third party.
To use this setup a user would have to have their own WordPress site (not wordpress.org)
Once a user buys the plugin they would install it and use the scripts in Second Life if they want to post listings and update rental information on the site. Or they can simply post it directly to the website if they wish of course.
Since this is a plugin, this would have it's own theme with child-theme capabilities for end-user customization.
Both ideas include a multitude of datafields and other cool stuff I've been developing. As far as third party interaction goes, every listing is entered by YOU, no one else. Idea 1 only gives you a publicly-searchable area to do so and Idea 2 lets you have full flexability to do what you wish.
Granted, I understand that most users such as I can simply throw up a simple website and use it for listings, but this system is geared towards total flexability, searchability, and ease of use for both the end-user and his/her customers.
Here's the video that shows the extra data that I'll be utilizing, I hope this is enough to excite at least a few people due to the fact that it's more "searchable" data than any site I have come across: http://www.jjswebs.com/second-life-real-estate-for-wordpress
if you need me to clarify any more please just let me know.