Most descriptions of how a business is sold are written by people who do it for a living, which makes them accurate and slightly misleading. The diagram is right and the experience is different: the slow parts are not where you expect, the emotional part is real and rarely mentioned, and the single most useful thing is unglamorous. This is the same process described the way owners who have been through it tend to describe it afterwards.
It starts long before there is a buyer
The work that determines how the sale goes happens while nothing is happening: assembling records, finding out what you cannot find, and writing down how the business runs when you are not there. Owners who start this when a buyer appears are already behind, and the buyer can tell, which affects both the timetable and the price they think they are paying for.
The middle is a document exercise, not a negotiation
Between agreeing a price in principle and completing, the great majority of the effort is the buyer asking for things and you providing them. It is administrative, it goes on longer than anyone expects, and it is where the sale either keeps its momentum or loses it. Nothing about this stage is intellectually hard and it consumes most of the calendar.
The part nobody mentions
Selling the business is also leaving it, and owners are frequently surprised by how that feels while trying to run the place normally through months of scrutiny. Practical consequence rather than sentiment: decide early who else can answer diligence questions, because being the only person who can is what makes the process exhausting. The consequence for the timetable is that owners who plan for a sale to be mostly negotiation plan the wrong period. Budget the months for administration and the days for the two conversations, and the whole thing becomes recognisable rather than surprising.
Questions people ask about how do you sell a business
Should I tell my staff?
Timing this is a judgement about your business and your people, and owners take opposite views for good reasons. What is worth planning either way is who besides you can answer a buyer's questions, because that is the practical constraint.
What surprises owners most?
How much of it is paperwork, and how long diligence takes. Almost nobody is surprised by the negotiation.
What is the one thing to do first?
Find out which documents you do not hold. It is a short exercise and it is the only one that changes the timetable rather than the workload.