“Reputable business is rarely conducted at a ‘bar’ (unless you are a lawyer, and that sort of ‘bar’ doesn’t serve food and drinks). So your question is really about going to a treff [sic] restaurant.”
This is not true. Many people hold business meetings in bars, or sometimes a firm will hold a social get-together which is technically not mandatory, but it will look bad if you don’t come. The most common example I can think of would be a journalist who takes his/her interview subject to a bar (a more casual atmosphere to make the interviewee feel at ease and open up to the questions).