Why even try this? You can refund games within two hours of gametime or two weeks from purchase date. The moment someone launches the game, it's immediatley obvious that it's not Helldivers and smashes that refund button.
If a kid’s got their parent’s credit card, I doubt they will bother with requesting a refund. They’ll just smash other ‘buy’ buttons until the game they want is downloaded.
I’m sure some adults are like this, too…
It's going to get reported and found by Steam pretty quickly. Steam already holds onto the money from sales for 2 weeks in case they need to issue a refund. Once they discover the scam, which will take less than a week, they won't hand over any of the money.
There's probably a decent number of people that buy a game and don't install it immediately. I often do this when something is on sale. By the time they realize they didn't get what they were after, it may be outside the refund window.