@Alison M. Some people really need to think about it, have their lawyer review the contact, or call around to get other offers (this gives the seller a sense of comfort when they see all offers are around what you are offering). If offers are close seller will them choose the person who they like & trust the most. @Kevin Brown is successful in getting the deals because his process creates trust with the seller and walking them through the contract gives him favor with the seller as well. He also uses the standard contract which helps when the seller has contract reviewed or remembers what the contract looked like last time they sold.
If the seller is semi motivated, I will follow up with them every couple weeks or month. You will notice the motivation increasing each time you talk to them. Some deals take a while to close and patience is the key. Focus on getting the seller to like you more than the competition, which I'm sure you have no problem with. In addition to you normal deals, you will now have a funnel of people who call you months later to sell to you.