Investors- Purchase & Sales Agreement vs. Letter of Intent?

[David Frandsen]

Hello BP investors. I have heard of investors keeping sales agreements in their car and making deals directly with sellers. I like this approach because I feel that when a seller is ready to sell you need to lock it up. I have always used a real estate agent to purchase deals and I still intend to do this. My question though is do any investors use a simple purchase and sales agreement or a letter of intent to "lock in" the seller upon making an agreement? 

Let me hear what you guys are doing. Thanks!