Plaintiffs in the United States and the United Kingdom claim the dealer has failed to pay out some, or all, of the proceeds of works he sold on their behalf, while others allege that he sold works that he was not authorised to offer.
Sammons' assets have been frozen in the UK and his passport confiscated.
The firm Timothy Sammons Limited, was made bankrupt in February this year by HMRC and the company's website was recently taken down.
At the High Court, Sammons is being sued by the WH Smith family trust seeking to recover a £1.6m Canaletto he sold on its behalf in 2014 but allegedly failed to remit the proceeds.
In a second case being heard in London and New York, Stephanie Overton - a New Zealand collector - says Sammons failed to hand over the £7.1m proceeds following the sale of paintings to a number of New York dealers.
Timothy Sammons Limited is also mentioned in other similar lawsuits concerning the sale of:
- Van Gogh's Cows In The Meadow at Sotheby's in June 2014 for £380,000 on behalf of the Cummings Trust
- Henry Moore works consigned by the British collector Lady Corinne Green to Sammons in June 2013
- Paul Gauguin's Nature Morte a la Ceramique (1888) owned by the Detroit collector Ralph Booth II
Timothy Sammons, 59, a trained solicitor and former Sotheby's specialist, set up his own fine art agency in 1996. In the same year he brokered the sale of John Singer Sargent's painting Cashmere to the Bill Gates Foundation for a record-breaking £6.7m.