We can sometimes use knowledge of psychology and body language to identify the real movers and shakers but to be safe try and spot everyone involved and convince them all.
Whilst just a callow youth, I would tend to gravitate towards sales jobs because in my mind they were an easy option.
Here is a fascinating head game that can give you some great insight into persuading others. Would you would like to be a millionaire?
Imagine that I walk up to you and ask you to buy a puppy. The Puppy dog close is an oldie but a goodie.
You have a meeting set up with a firm of architects to demonstrate your stressed concrete roof trusses and realize that you have got the office junior.
In many persuasion, sales, and negotiating skills, books that I have read recently, the authors have all been at pains to point out that theirs is a gentle art.