The dinner is not the negotiation
A business dinner is arranged to see how people are, not to settle terms. Terms have a room of their own and a document with a date on it. What a dinner can do is let two houses find out whether they can sit together for two hours, which is information no document supplies.
So the guest who arrives with a folder, or who opens the matter over the fish, has misread the invitation and taken the evening hostage. The subject may be raised by the host, once, near the end, and briefly. A guest answers what is asked and no more, and may say that the rest belongs to the meeting, which is a sentence that makes a good impression rather than a bad one.
Who hosts, and who sits where
Whoever issued the invitation hosts, and the host settles the room, the table and the pace. A guest arrives at the hour stated, gives a coat to whoever takes it, and does not rearrange the seating by sitting elsewhere. Where cards are set, the card is the instruction; where they are not, the guest waits to be placed.
The host sits where service can reach them, usually with their back to the wall, and places the most senior guest on the right. The most junior person present is seated where the host can speak to them, which is a courtesy rather than an afterthought: the quietest person at a business dinner is often the one who will do the work.
What is talked about
Everything except the matter in hand, money, illness, politics and the faults of a previous employer. Good subjects are the ones where a person can be generous: a building, a city, a journey, something recently read, the food on the table. A question about someone’s work is welcome where it is about the work rather than their position in it.
Questions are better than opinions. An opinion offered early divides a table; a question asked well gives each person something to be good at. Where a subject turns awkward, the host moves it with one small practical sentence about the room or the wine, and the table is grateful for the interruption.
Drink, and the one glass rule
One glass, held slowly, is the whole of the professional discipline at a business table. A second is a decision and a third is a different evening. Water is drunk in between and nobody remarks on it. A guest who does not drink says so once, plainly, and a host who offers twice is the one who has been rude.
The reason is not moral. A business dinner is remembered for what a person said, and the person who remembers least of the evening is usually the one whose evening it spoiled. Restraint at the table reads as competence, because it is.
The end, and the note
The host ends the evening, not the guest. A guest watches for the signal, thanks the host at the door by name, and leaves without a long goodbye. If a car was arranged it is taken; if not, thanks are given inside and not in the street.
A written note within the day, two sentences, is the mark of a house rather than of a company: one thing about the evening, and thanks. A card is better than an email and either is better than silence. It will be read by the host’s assistant before the host sees it, which is a reason to write it carefully rather than a reason not to write it at all.