One of the most frustrating buy-in failures is when you need the agreement of someone who is actually not negatively affected by the problem, perhaps barely associated with it, but they have a crucial role in the buy-in - even if that role is simply to get out of the way, and not block the implementation of a plan.
In that situation, a variation of the buy-in process is used to create the "what's in it for them" picture.
This method is also the base approach when persuading anyone in circumstances when you don't have the suite of buy-in tools with you. By focusing on the "WIIFT" your odds of success are automatically several notches higher than most conventional approaches.
For an outside person - they're not involved in the subject matter, but you need their buy-in to make the solution fly
For example, a bank manager.
1. Identify the actions you think the other person should take (in support of your cause).
2. Identify the "what's in it for them" aspects that will emerge from them taking the actions you want them to take. We call these "Desirable Effects," or DE's.
3. Build a FRT starting with the actions in #1 and building up to the DE's in #2 above.
4. Carefully review the FRT, looking for any entities on the tree that the person is unlikely to accept, based on their experience.
5. If there are any then for each of them, plot the sequence of a presentation or discussion that will persuade them and thereby ensure their acceptance of the issues identified in #4.
6. When you meet, start with these presentations or discussions, and only when complete should you then expose the FRT ... but do it from the top down, i.e. starting with "What's In It For Him."
Note: If you have to gain the buy-in of someone, regardless of their position, and you do NOT have a CRT to use, the approach for an Outside Person is the best approach.