A lot of games come with a sample scenario or two in the back that functions as an introduction to the game. If you start a new game of some kind (something more obscure I mean, not like Pathfinder or whatever) and intend to run the sample scenario as an introduction to the game for everyone, the other players are going to have every opportunity to read the adventure and know what happens/what they have to do. There's not much you can do to prevent his, not if you expect your players to know anything about the rules when you start anyway. All you can really do tell them, "hey we're going to play the sample in the back. While you're learning the rules between now and gametime please refrain from reading it." Do you think your ordinary, random PUG player that you've never met before can be trusted to be honest and not read the adventure?
