A simple social media post ended up costing one Boston Red Sox baseball fan a big amount of money.

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Robbie Johnson, a 28-year-old after-school instructor from Wellesley. Massachusetts, got tickets for Game 2 of the World Series and, as most people are inclined to do, posted a picture on Instagram.

When he arrived at Fenway Park on Wednesday with his sister, the $650 ticket his family bought for him did not work.

"I went to ticket services and that's where I was informed [the] ticket had been scanned at 5:09 p.m, a couple of hours before we got there," Johnson said.

Someone stole his seat. But how?

What a lot of people don't realize is that all the information a scam artist needs to make a duplicate of a concert or sporting event ticket is printed on it.

A Boston fan's ticket to Game 2 of the World Series was used by someone who saw it posted to social media.

Credit: Boston25News.com

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Credit: Boston25News.com

The picture of the ticket Johnson posted on Instagram included the bar code and his unique ticket number. With that information, someone turned Johnson's ticket into a free entry to a World Series game.

According to April Martin, community outreach manager for Ace Tickets, the ticket company recently began warning customers about this type of theft.

"You can post your ticket, you just need to make sure you cover it -- the bar code especially and even your seating location," Martin said.

Johnson ended up getting into the game after all, but not without dropping $450 for a second ticket.

He said the person who went in with his original seat number never sat in the seat.

"There are people who will do these things, which is unfortunate," Martin added. "We were very excited about it, never been to a World Series [and it has] always been a lifelong dream of both of ours."

Since the scam, Johnson has made his Instagram feed private.