I'd be very cautious with this seller. I previously noticed he was selling a Favre gamer, which seemed off as the NFL Equipment logo would have it as being pre-2008. Not 2009 as the tagging suggests:
http://www.ebay.com/itm/Minnesota-Vikin ... 231466838b
I checked his buying history and sure enough noticed this:
This confirms the jersey was from 2006 and therefore likely a blank gamer which was customized. He's also changed the size tagging to be a 52 (i.e. Favre's size) even although the jersey is presumably a size 46.
All in all, his jerseys are legit, but most likely to be blank customizations or re-tagged gamers. Nothing criminal about this, but the language in his postings is deliberately mis-leading (i.e. "This happens to be Favre's 1st year with the Vikings to where he almost took them to the Superbowl") so you probably wouldn't be getting exactly what you're paying (a premium) for.