Why there are same script selling in different sites?
You can find complete details about the script piracy by clicking here. Just to be clear, any script similar, exact looking script is nulled/pirated if found anywhere else then snetworksclassifieds.com's own website. Most cases, the script's are reversed engineered by modifying with harmful programming codes which creates very high risk of security hole into your script. And most likely will get hacked easily.
It is advised not to use pirated or illegal copies of SNetworks PHP Classifieds script since you may start using fine but will not receive any support or regular updates/upgrades of the script and shall make your site vulnerable online.