The problem with ordering ancient, outdated software such as CS6 from 3rd party vendors is that you've got no idea if
- the software on the disk is counterfeit, hack-free or virus-free apart from the credibility of the vendor and
- you've got no idea if the serial number which comes with the DVD is valid (i.e counterfeit) until you enter it when you install the software. If Adobe rejects it as an invalid serial number, your only recourse is to go back to the vendor for a refund with the shrinkwrap removed and the packaging opened which usually invalidates a refund. You could end up in a costly world of hurt chasing a refund.
As always, caveat emptor.
Why Not to Buy Adobe Software on eBay, Craigslist or Amazon Mkt | ProDesignTools
Are you specifically avoiding the subscription route for a reason? What are your computer specs? Which Adobe software would you be using and for what purposes?