Germany ? - banging heads together
I've been working with and installing ERP systems for 31 years now and have worked out that by the time you have to bang heads together it is all a bit too late in the day and as you rightly pointed out there is around a 50% chance that it is your own head that will get banged
Without a fundamental buy in by the owner/ceo/equivalent then the managers down the tree will start to make their own decisions and possibly 'walk away' from the project when the going gets tough.
The first conversation to be had with the owner/ceo is that if they are not prepared to give their commitment to the project and support this through doing the appropriate head banging then the project should never start.
Anyone on the supply chain will NEVER have this conversation with the owner/ceo because they fear they will lose the sale. They spot this lack of buy in as a money making opportunity and are very much aware that confusion will occur down the line and will protect themselves at all costs. Many Consultancies have made a lot of money over the years by being past masters at fleecing the Customer. They have had years of experience in doing it whilst the Customer is still relatively inexerienced.