At the very least they need to provide the Windows license key if not the media for it too. For the price they charge all the software should be legit. If not and they are selling machines cutting corners on the Windows license then you can use this site to report.
https://reporting.bsa.org/r/report/add.aspx?src=us&ln=en-us
Without the media or at least a backup you're SOL if you ever have to recover from scratch.