You can download CS-Cart and test it for 30 days. The trial version is 100% functional, you will have access to all the tools and functionality.
When the trial period is over, the admin panel will be blocked, you will be prompted to purchase a license.
If you would like to proceed with bulding your store on CS-Cart or Multi-Vendor, no need in reinstaling the software. Just purchase a license (CS-Cart or Multi-Vendor) and enter it to your test install to unlock the admin panel. All your changes will be saved.