I don't know German produce but I'm pretty confident California, where I'm from, doesn't compare to Paris' farmers markets. The variety and quality there were way beyond all the farmers markets and produce stands I've been to over my life in California. That said, I certainly noticed a difference between California and Maryland, at least at the time. But, having experienced better I no longer consider California good. As one example, I have very bad luck trying to find a tomato with any flavor.

In the US, a lot of "farmers" markets are just people selling wholesale produce they bought from a warehouse or maybe Costco or similar. There's not really any regulation (though I don't know about California, specifically).