The most useful contribution an M&A advisor can make to a client is, occasionally, the recommendation to walk from a transaction. This is rarely a popular recommendation, and is rarely the recommendation the advisor's economics encourage. It is, however, the recommendation the long-term relationship requires.
I have made the recommendation twice in the last three years. On both occasions the client was reluctant; on both occasions the client accepted it; on both occasions the eighteen months that followed produced more than enough confirmation that the recommendation had been correct. The transactions that we walked from would have proceeded if the diligence had been conducted on the seller's preferred timeline and with the typical buyer's appetite for finding reasons to do the deal that brought the buyer to the table.
The discipline of walking is not principally an analytical discipline. The analysis usually surfaces the relevant facts. The discipline is the willingness to act on the analysis when the act is unpopular with the client and uncomfortable for the advisor — and to do so without the bluster or the rhetoric that lesser advisors substitute for it. The transactions that should be walked from are, in our experience, identifiable by the diligence team that has been given the time to do its work. The transactions that are walked from are the ones whose advisors are willing to make the recommendation when they should.