Very true, in addition it can still be done by keeping records of the past milestones you have achieved or showing records if similar problems you solved in the past, that could actually go a long way in convincing the potential customers/clients.
It is fine to give suggestions or recommendations in solving business problems based on our work experiences. However, we need to be more objective than subjective. You can do this by providing statistics or findings about certain business problems. In this way, it would be easier to convince our co-workers. But then, we still need to be opened to other resolutions that can be given by them.