First, I'd like to say you are on the right track as a producer to get in the mindset of selling beats exclusively rather than lease them.
I never understood why producers would put work into something they are going to nickel and dime. And if you really think about it, what artist in their right mind is going to spend money on an instrumental that a score of others are going to be using the exact same beat?
As for the process of selling exclusively, the way I work it is to have a "portfolio" of beats to let the artist listen to. This lets them hear your style.
When I make music, I put effort into designing an overall sound that evokes an emotion. If the beat don't have feeling behind it, no one is gonna "feel it". So I put together about 10-12 high quality beats that each have a different persona.
Then I ask them questions about what their upcoming projects are like. Is their a theme? What's the message? What mood do you want the listener feeling? Is there anything you've heard that I played for you that has a similar vibe to what you want?
A lot of the time they say "oh I really like that one". And great, that beat can get sold to them. But sometimes they like a certain style and what to add their own twist and will actually tell you what they want. So you have to do a good job in asking probing questions and being a good listener to decipher what it is they want.
Before I start working on a beat, or touching up a beat I have that is already in the works. I ask for a 1/3 deposit and have them sign my EXCLUSIVE BEAT LICENSE AGREEMENT.
Then work begins and my turn around is usually 1-2 weeks. I like to take my time to deliver a quality product. If you just throw things together they aren't going to be happy and are going to ask you to change this or that and you'll actually have more work than if you just took time from the beginning.
If the artist is local, I deliver the beat on CD, which contains an MP3 version, a .wav file, and a folder with all the sounds tracked out as .wav clips that they can bring to the studio.
If I'm working remotely with someone through online means, I package all that in a zip file and email it to them.
My agreement states that "final balance is due within 10 days of delivery of master recording."
Having a PayPal or Google Checkout account makes pay arrangements run smoothly for online transactions. I take cash/check with local artists.