Craigslist Seller with Mac Pro S/N of Quad Core, but 12-Core Inside . . . Is it Scary?

I'm looking to buy a used Mac Pro, 2010 for Photoshop, graphics & web work. I'm looking for something with a Geekbench 3.0/64 above 15,000. I found a 5,1 12-Core (https://everymac.com/systems/apple/mac_pro/specs/mac-pro-twelve-core-2.66-mid-20 10-westmere-specs.html) on Craigslist with a Geekbench of 25,131 and met the seller who has a lot of Mac Pros for sale. He seemed very knowledgeable but I noticed the S/N was not for that model so I asked why the case has a S/N for a 2010 Quad Core Xeon 2.4GHz, but the guts are from a Westmere 12-Core. "About This Mac" shows it to be a 12-Core with the right graphics card

He said the 2010 cases are interchangeable and the case the 12-Core was in was badly scratched so he swapped them to increase its value. Do you think there is a concern about this? I know some eBayers do upgrades from 2008 & '09s that won't run the Current OS to systems with firmware updates & hacks that will.

This doesn't _appear_ to be the case, but I'm asking, if "About This Mac" is showing the right specs and the Geekbench is good and it boots normally without any apparent hacks and its performance is compatible with the specs . . . is this a scary purchase? What should I be wary of? He seems legit, but the S/N is a bother.

The price is appropriate for this model about $1200.

Thanks!

Joel

Atlanta, GA