How does earnest money deposits works? As I was reading, I saw that when dealing with new buyers many wholesalers had made the buyers pay an earnest money deposit. Is this a recommended practice? Why? How much do I ask for when requiring a earnest money deposit?

The reason is that I'm looking to expand with dealing with notes as a broker into wholesaling real estate as my entry to being a real estate investor. I took Financexaminer's advice to read through key points in Wests Business Law Text book, and I feel as though have a better grasp on Laws and ethics.

Now to start, I have been researching the art of wholesale here in BiggerPockets, and boy was there alot to read and learn. I even expanded to outside resources such as the library and other internet resources to solidify information and get more perspective of wholesaling.

I feel I got a grasp on how the wholesaling process works in terms of finding buyers and the homes when dealing directly with the home owner. However, I don't feel comfortable interacting with realtors until I'm more experienced. I think I need to somehow make a script to study so my answers to those hard questions won't begin with "uhh" and end with "umm".

What I don't know are the little gaps in information, such as How do I pre-screen a buyer to see if he's good? or How do I introduce myself to a potential prospects?. Another question was how do I start wholesaling "virtually"?

I know I have a bad tendency of over explaining myself and I asking alot of questions, so to start somewhere basic, Could someone explain Earnest Money Deposits?
I mean, If you have the answers to my other questions then by all means I ask for the answers plus tips. I'm looking to absorb and retain any and all quality information, to learn everything I can to be successful.