Some online agencies were selling tickets for up to £200 for the wrong dates and cities he is not playing.
Tour agent Ian Huffam said the singer "would like to disassociate himself 100 per cent from rogue ticket agencies".
Williams' tour begins in South Africa next April and includes shows in Leeds and Glasgow. It ends with two nights at Wembley Stadium in September.
Wembley Stadium, London - 14 & 15 September
In Ireland, Williams will appear in Dublin but no date has yet been confirmed.
Before the tour was confirmed, several online ticket agencies were selling tickets for shows in Glasgow, Manchester, London and Cardiff in July 2006.
But Williams will actually be playing in Glasgow, Leeds and London in September.
Michael Rangos, managing director of Getmetickets.net, said fans booking tickets for unconfirmed dates were clearly warned the dates were provisional and subject to change.
He said customers who had already booked could now select which confirmed date they wanted tickets for - but could not get a refund.
"People were fully aware," he said. "The face value is clear, the price they're paying is clear, the provisionality is clear.
"No one is being ripped off or misled. There's no misunderstanding."
He said the company only sold tickets for unconfirmed dates because people were "begging to book".
The section selling tickets for the tour on Williams' website was temporarily suspended on Wednesday morning.
Fans attempting to make purchases though the site experienced difficulties because of the massive demand.
The website wrongly stated that some venues were sold out.
The service was suspended while a backlog of payments was processed but is now operating normally.