Martínez was identified as the seller of a Mark Rothko's "Untitled" (1961) at Sotheby's in a 2010 lawsuit against him by Dallas art collector Marguerite Hoffman, who claimed breach of contract. Hoffman sold him the work privately in 2007 for a net $17.6 million, forgoing the $30 million to $40 million she said the painting could have fetched at public auction. She later said the deal's privacy agreement was broken when Studio Capital Inc., a Belize-registered company she claimed is controlled by Martínez "for the purpose of maintaining the secrecy of his purchases and sales of art," entered the Rothko in Sotheby's May 2010 auction in New York and marketing materials revealed her prior ownership. She claimed she could have sold the painting at auction herself and received far more, had she not wanted secrecy. The painting was auctioned for $31.4 million.