Mark Bonnici from Machen, Caerphilly, also said he had no reason not to trust Mr Gray, whom he said he had known for years.
He paid £1,200 for four tickets and said the experience had left him feeling "sick".
Mr Gray had previously offered him hospitality tickets for the rugby, which he went to without issues.
When he asked him if he was interested in Oasis tickets, Mr Bonnici said yes and transferred the money.
"He said his phone was playing up and he couldn't transfer the tickets," Mr Bonnici said.
Like Mr Stephens, he was told to meet Mr Gray outside gate three of the stadium.
"There was no sign of him and his phone has been switched off ever since," he said.
Mr Stephens decided to call the hospitality account manager for the Principality Stadium on the Saturday morning, while on his way into Cardiff to try to find out whether his tickets were genuine.
"He broke the rather unfortunate news that the booking didn't exist in his name," he said.
The WRU has been asked whether or not Mr Gray has ever held a box at the Principality Stadium.
"I was annoyed, my wife was inconsolable. She was so looking forward to this," said Mr Stephens.
"As the day unfolded, it became very clear through a series of Facebook posts that not only did he sell 33 seats for the one box, he sold it over and over and over.
"The last count as of this (Monday) morning was 87 tickets. A lot of very angry people".
Mr Bonnici also said it only became clear many others had been affected after his daughter posted on social media and contacted hospitality at the Principality Stadium.
Large groups of other people had been waiting for their tickets in the same location, he said.
"I'm probably more disappointed than anything," he said. "This is someone I know, I've known for years."
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