Christoph Gottschalk's firm Dolche Media earned millions from contracts with Daimler-Chrysler and Solarworld which Der Spiegel news magazine said included detailed agreements about how their products were to be promoted on the show.
The mix of chat, celebrities and challenges has long been a staple on the German television landscape, attracting audiences of up to ten million for state TV station ZDF - and for 24 years was hosted by Gottschalk. He left in 2011 after a stunt went wrong leaving a member of the public paralysed.
The presenter and his brother owned Dolche Media which in 2003 signed a three-year contract with Daimler. Der Spiegel said the deal laid out in detail how a special model of the Mercedes A-class car would be introduced, how long the car would be shown and how it would be presented.
Such contracts contradict ZDF's public broadcasting remit - and it said on Sunday it had no information that "surreptitious advertising in connection took place with the presentation of competition prices on Wetten, dass..? a spokesman said - adding that the allegations would be investigated.
Daimler paid €1.25 million plus VAT for the deal and considered it a completely normal procedure, the magazine said. Thomas Gottschalk was also given "access" to a top-class car, according to Daimler. A spokesman for the auto giant said it had depended on Dolche Media to ensure that the advertising and sponsoring guidelines of ZDF were respected.
German solar energy firm Solarworld also paid around €1 million to be cooperation partner with the show. Solarworld boss Frank Asbeck said he was "very satisfied - it was a super programme spot and we had a great advertising effect."
Der Spiegel quoted media and advertising expert Gero Himmelsbach who said details of how a product should be introduced being a contract showed that it was the "banned surreptitious advertising" rather than simply donating a prize. The magazine noted that Audi has been cooperation partner with the show since 2007.
ZDF director Thomas Bellut said such cooperation would not be repeated. "That the brand rights for Wetten, dass..? were externally marketed to this degree was also due to the fact that Gottschalk was so important for the broadcaster at that time."
He said the contract with Audi was due to expire this summer and that then Dolce Media would no longer be responsible for organising the prizes.
"The marketing of the brand rights and the acquisition of game prizes will after Gottschalk, no longer be in one hand," said Bellut.
"It damages the broadcaster if there is even just the appearance that things are not clean," he said.