Ask for payment. This will quickly sort out if a product solves a problem that people care about.
"You want a lot of things. You want an A in this class. You want a trip to Hawaii. You want a tasty lunch. And you want all of those things ... 'a lot.' Well, I'm economist, I'm trying to be a scientist. I can't measure 'a lot.' What I can measure is - what are you willing to give up in order to get the things you want?"
I didn't take economics at Uni, but I certainly noticed a corollary of 'desire' for object and payment as a kid. The lack of money required you work out some scheme to make money to buy or your hack your own.