Musannaf Ibn Abi Shayba 13:1188

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Ibn ‘Awn, from Ibn Sirin, that he used to say: A man may mark his goods as he wishes, then say: "I only marked it so that I may bargain with you over it," then he sells it by decreasing [the price], such as ten for nine.