I have one like this and with the proper handloads it's good for .33MOA consistently... That barrel cost me $600 IIRC so this is a steal, too bad I can't use another. I'd jump on this in a heartbeat if you need a really good Grendel barrel for sure. You sure won't be disappointed.
If he's getting .5MOA with factory loads or Hornady 123's, that's about the norm it seems... I get the best groups after Bill A. turned me onto 120BT handloads and he was also using a 20" Satern bbl.
Good luck with your sale.