Trading standards officials in Cardiff are warning rugby fans about the risks of buying World Cup tickets online.
Tickets are still available for the Wales versus Japan match
With a week before the tournament kicks off in France, thousands of tickets are on offer on unofficial websites.
Most tickets via official sources have already been sold and one fans' website says supporters will still buy online.
But Cardiff Council's Handley Brustad said: "Quite often these tickets just don't materialise, it's a pure scam for you to send money."
Cardiff's Millennium Stadium is hosting four Rugby World Cup matches and organisers say there are still plenty of tickets left for two games - Wales versus Japan and Canada versus Fiji.
Rugby World Cup organisers say match tickets can only be bought through their official sources.
They warn that people who buy through other outlets run the risk of having their tickets cancelled, being refused entry to games or even being expelled from the stadium.
However, Dan Allsobrook, who organises a Welsh fans' website says there will still be online activity this weekend by supporters desperate to see Wales play and who are prepared to pay well over the odds for the bigger games.
He said: "They're just resigned to the fact they they're going to have to pay unofficially, either online or to a tout on the street.
"And now is the time when people are really starting to get nervous about the tickets, having the hotel and train or ferry tickets booked months before."
But trading standards officials say buying from unofficial sources carries a risk of being ripped off.
Mr Brustad, a senior trading standards officer, said: "The pitfalls of using unofficial sites is you don't know who you're dealing with in most instances.
"You are totally in the hands of someone, somewhere that you don't know, sending you a ticket or directing you to a box office somewhere.
"We've seen it happen where on many occasions people have bought on the internet and they've have been told that their ticket is awaiting them at the box office or someone is stood outside waiting to hand the tickets over.
"And on these occasions there is no ticket.
"My advice to anyone that wants to buy a ticket over the internet is only use the official ticket sources.
"That is the only way you can guarantee entry to the game and ensure that the ticket you are buying is a genuine ticket and will arrive."