In your sales pitch, lead them to the following question: “Now that you know so much about the product, what do you think is the price I am selling this for?” Don’t ask what they think you should sell it for, but what do they think you are selling it for. Most likely they will give a good guess, and by doing so publicly commit to it. If you know give them a price that is close (either higher or lower), they will be more likely to accept it as a fair price. This can be done face to face, on the phone, or on a web page.
A game you can play by yourself anytime anywhere.
An app is running in the background. At random times during your active hours, it will alert you with a prompt to guess the time. You input the time you think it is, and it will show you how accurate you are. The more you play, the better you’ll get, and you can see your progress in the app.
A fun game to discover interesting designs and artifacts.
Publish a daily photo or video of seemingly simple objects and let people guess (not public until the end of the day) what they are. At the end of the day, the people who guessed right are listed in chronological order. The first 30% of these get points. The leaderboard of best guesses is updated daily.