While this is an extreme example, it is a common challenge for many service-focused businesses. People buy your service without being able to see the end result. And this can be made worse by misaligned expectations. The client thinks you are delivering one thing and they get another.
One of the best ways to minimize this challenge is to have a defined system. This can include a diagram, description of each step and defined deliverables, often with an example. Defining your process does two things: First, it gives prospects something tangible. Second, it demonstrates that you have worked with enough clients with similar needs that you have developed a process that works across different clients.
This works much better than a custom proposal, because you can get much clearer describing each step and the client is less likely to have a preconceived idea of what they would be getting. So, they pay more attention to the deliverables you lay out. Even if they end up wanting a custom proposal, it is now clear what you typically deliver and any customization can be described in relation to the typical process.
So if you want to improve your sales process for you and your prospects, consider developing a defined process for the service you offer. It will make it easier for prospects to say “yes.”