High value professional services are tricky things. You can rarely trial them prior to consumption; by definition they are likely to be expensive (yet could offer great value) and often they are intangible. Given this, they are difficult things to sell or market.
Central to the challenge is an absolute requirement to establish trust in the provider. Establishing that trust is likely to be a multi-layered process. It could well involve a cocktail of proven experience, an established organisation, external references and recommendation and of course personal judgement. There could be other factors at play in terms of being seen as a 'thought leader', or very practical issues such as contractual terms. All of these should lead to a conclusion that the provider can provide the service to the buyer's satisfaction and ideally add something unique or different.
The trust issue is one that is not always understood by professional service marketers. Marketing is a tool kit that needs to be adapted to suit circumstances and market conditions, and differing sales processes require an appropriate tactical balance. I have completed quite a few consultancy projects that broadly come with the same brief; 'We have a marketing team and they are busy but we do not seem to benefiting much from it?' Often the result of the investigation is that the team – whilst talented – are managing things they like or understand and not focused enough on supporting things that are required to aid the core sales process.