So they're making tactical mistakes, or forgetting rules. As long as they have a good time. There will always be time to learn the rules correctly later on. Problem players, such as the guy who already knows the rules and is trying to catch you in a mistake, will come in from time to time. Label your books and miniatures and keep an eye on them.
Most people are honest, but sadly there are rotten apples in every basket.
Don't get angry. Sometimes it's good to vent, but a demo is not the place for it. In exchange for your time and effort, we are offering you DP9 credits. Here's how the credit system works. We have attached a report sheet at the end of this manual.