how to tell what software made a website?

This is a real general question. i have someone who wants me to design a site for vacation rentals. this site would need to have the ability for the customers putting their own cabins, houses, property on themselves and then be able to pay via paypal etc... for the particular listing. an example of this would be www.vacationrentals.com.
I don't think that zen cart is capable of this but how do i find out what software was used to create vacationrentals.com website?
or does anyone know of a software / cart / phpscript / asp script that would allow a full admin section for the web designer and another admin/backend section that would allow customers to add their own properties, description, etc..?

i've searched all over the web for vaction rental software / scripts, etc and have not found a viable solution but i know they are out there because there are too many vacation rental websites out there that allow you to do this.

any information would be greatly appreciated.

thanks!!

It is possible that the script are custom made and the copyright is held by the owner of the site or the developer of such scripts.

Even though there are many rental sites out there doesnt mean they are all using the same script btw.

Also, it's not easy to tell what software is used. For example if someone is familiar with zen, then they may notice a site is using zen based on the form of the urls generated etc... But that's about it.

Google is a powerful tool

http://www.google.com/search?q=rental+scripts&start=0&ie=utf-8&oe=utf-8&client=firefox-a&rls=org.mozilla:en-US:official