Complex sentence: In 2008, Graff took a daring chance by purchasing the Wittelsbach Diamond for 16.4 million pounds Sterling, which was a considerable premium over the 9 million pounds Sterling guide price.
Split into simpler sentences: In 2008, Graff took a daring chance. He purchased the Wittelsbach Diamond for 16.4 million pounds Sterling, which was a considerable premium over the 9 million pounds Sterling guide price.