There are a few considerations and here is a general framework for this type of valuation exercise.
1. Who is the end user and for what purpose? The level of detail and sophistication needed, skewing to the high or the low side, and as a comparison to what situation? Is the transaction a sale to a competitor, an immediate liquidation, etc.?
2. A strong set of current data, information, and projections is needed. Sometimes private companies need help in getting to the point where there is a strong enough information base to begin.
2a. Information about the industry, competition, product positioning in consumers and retailers minds
3. Then different valuation methods will be applied. Discounted cash flow analysis, comparable transactions, common sense, control premiums, comparable companies, and then sometimes reality. The valuation can often come from the best offer on the table.