Copied this information from their website and should answer your question. They are a third party shopping service that purchases the merchandise from the pro shop and ships it to you the customer.

The 2021 Masters Tournament merchandise is here! MMO Golf is your one stop shop for purchasing official Augusta National Masters Merchandise online. We ship directly to your door all around the world! All items listed online are IN-STOCK items and being shipped daily!

Please allow 1-3 business days to ship including Next Day Air and 2nd Day Air shipments. Call 888.660.7910 for expedited shipping arrangements.

Please note: MMO Golf is not affiliated with the US Open, United States Golf Association (USGA), www.Masters.com, Masters.org or Augusta National. "We are a third party "shopping service" that purchases the product from the pro shop and ships it to you all over the world".

They are being offered at the Masters Online Shop, which is open to ticketed patrons only (even if they didn’t get the limited tickets offered this year). They ARE NOT $139/dozen on the sanctioned site. So, they are either fake or being resold at a premium (which is frowned upon by the powers to be in Augusta).

I have some Masters ProV1s from when I attended a few years ago. These are typically only available in the Augusta National pro shop, but there are a lot of people who buy a ton of merchandise for resell. It sounds like that is what is happening here.

I’ve never been to Augusta, hope to go one day. Those prices seem outrageous. $229 for a Peter Millar polo, $79 for a t shirt?

Yeah, the resellers are putting a huge mark up on their stuff. I went in 2011 and thought the prices were very reasonable in the merchandise tent.

And you can have your stuff shipped to your house. When you get to the end of the line they had a FedEx station set up. Well run operation.

The pro shop prices during the Masters is comparable to any premium pro shop in the country. Most people don't play top 100 courses regularly, so they are shocked at prices, but the prices there are pretty standard and fair. The food is the biggest bargain in the country!!

The merchandise prices at the Augusta on course shop are fair. Nowhere near what the online pirates get.