In short, you must commit time, money and a lot of creativity to finding notes, anything less will cause you to fail. This advice probably holds true for much of one's success in life. The note business is a people business above all else. Unless you can handle the note seller in a professional manner, they will not sell you their note. We are dealing, for many note sellers, with the most money they have ever seen in their lives and if they do not trust you all the calculator and marketing skills in the world will do you no good at all.
Negotiation is another word for credibility or rapport.
You will never buy a note from someone who does not trust you. To be an advanced note broker you must be able to establish your credibility immediately. The note seller must know that you know the business, that you can really buy their note and that you will treat them fairly. If you miss a step on any of those you have almost certainly lost the deal. The good news is you can learn the skill of negotiation by taking a class, reading a book and being aware of how you affect other people.