English spoken by those who do not share their first language is increasingly referred to as English lingua franca (ELF). For ELF speakers, it can be a challenge to express conflicting opinions, as a common language and/or cultural background cannot be taken for granted. This is recognized by writers of business English textbooks, who provide advice concerning ways to express disagreement. The present paper analyses this advice based on 13 textbooks aimed at the upper intermediate/advanced level business student and compares their recommendations with ELF usage among business students at this level of proficiency. The ELF corpus used consists of 25 simulated negotiations, total time 6 h 38 min. Six of the negotiations were carried out as a course activity and 19 as part of an oral exam. My main finding is that there was little correspondence between the actual formulations recommended in the textbooks and ELF usage. However, the strategic approach implicit in the textbook advice was predominantly one of mitigation, which was also the dominant approach used by the ELF speakers in my corpus.