I couldn't agree more - this is NOT a decision a business owner should make alone.
While it's true that the best time to sell is when the business is doing well, very often significant value can be added to the business. As a Certified Value Builder as well as a licensed business broker, I work with business owners in a SWOT analysis (strengths, weaknesses, opportunities, and threats) to assess the current value of the business and develop a strategic plan, with precise tactical steps, to vastly increase the value of their business over the course of 12-18 months. Then we determine if the time and expense is worth it, or if it's better to sell in the current market.
Sometimes it makes sense to list the business for sale, anticipating the value that will be realized in the next six to twelve months, and let the business "grow into" the asking price.
But, all of these decisions require the expertise of a professional business broker who also has experience and expertise in the hands-on process of business value development.