Eric provided a very good link. In that link is this statement
The embedded Cisco software that runs on the hardware—as well as Cisco standalone software—is not transferable unless specifically allowed under the Cisco Software License Transfer and Re-Use Policy. If you purchase used or secondary-market Cisco equipment, you must acquire a new license from Cisco before the software can be used.
I believe that I have seen similar statements in the paper work that we typically ignore as we unpack new Cisco gear. So technically it is a violation of the Terms of Service to purchase on EBAY and run it with the original license. I have not heard of attempts to enforce that restriction. And certainly there are lots of people who do purchase used equipment and run with the original license. But if you are in an organization which has internal policies about observing ToS then this would be an issue.
Usually, when you purchase Cisco devices on eBay, you are pretty much on your own when it comes to software upgrades and RMA especially when all these devices are EOL and EOS (the first 3 switches in the list). In addition, usually, Cisco partners will not sell your service contract on a product you did not purchase from them. So, if you are buying this for your organization, and for production, before you make this kind of purchase, ask your manager and get approval in writing