I'll look for it next time I'm at a game. I suspect that while authenticity isn't as huge a concern, prices - like everything else at a game - are too high.
This isn't baseball, obviously, but during my last visit to Lambeau Field several years ago, I did notice the Packers Pro Shop had some authentic signed books from current and past players (AJ Hawk and HOFer Jim Taylor). They were the book retail price.
Now that was one heck of a deal.
Fenway has a huge memorabilia store on Yawkey way, no doubt about authenticity but prices are very high.
Is the Fenway store a team-owned store?
Are all team memorabilia stores at stadiums team-owned or so they bring in vendors, too?
Has anyone seen forgeries offered by vendors at baseball games?
Some are owned by the team and other are concessions. Dodger Stadium, Anaheim Stadium and Staples Center all have memorabilia stores called Art of the Game. They are operated by a third party. However, my understanding is that autographs and game used items are provided by the team. The concessionaire does produce the presentation of the items. As you would expect, 95% of the items are associated with the home team. I have never seen anything for sale in either the stores at Dodgers Stadium or Anaheim Stadium that would cause any concern regarding authenticity. I have also never seen a single item that was priced in the same universe as the market price ($999 for a Mike Trout Autographed ball). I'm sure the concessionaire pays a pretty penny for the concession and I wouldn't be surprised if the team also gets a good chunk of sales. Like anything else in a ballpark, you're paying through the nose.
In Tampa (technically St. Pete) they have a team store with game-used and other signed memorabilia. The prices are high but no doubt about authenticity.
At their Fan Fest every year they hold a "yard sale" where they sell some game used items for much cheaper.
I haven't heard of a team outsourcing the autograph sales to an outside vendor. It wouldn't make much sense to me, either. You run an increased risk of a lawsuit via fraud, take in less profit because you give the dealer a cut and you have less control on customer satisfaction, etc. Plus, you own the team so acquiring the merchandise shouldn't be an issue.
The Mets have a store inside Citi Field where they sell memorabilia.
The strangest thing to me is that the game-worn jerseys are available off the rack, as opposed to being in a display case where you have to ask to see it. For example, this Matt Harvey game-worn jersey...
...which has an asking price of $2,500. You can take it off the rack yourself for a close-up look.
But I'm not complaining. Makes it easier for me to take pictures.