How many people would find that site in the process of searching for a flight sim for sale and question whether or not it's illegal to be selling what they're selling?

And of course how many of those who would question it would actually stop and NOT purchase it?

Unfortunately I think the majority of people wouldn't even question it. And of those that did question the legality would probably somehow justify that since it's being sold openly it must be legal to do so and purchase the product anyway.

Is it up to the American consumer (or World consumer) to enforce the law or is it up to the law enforcement officials to protect the public from the unlawful?

Laws are only as strong as the enforcement behind them. I'm not advocating breaking the law. But, let's be real. The site needs to be shut down by those responsible and until that happens, until the law steps in, those who purchase the product have only their moral compass to go by.