Challenging is a buying signal
When I started selling in DACH, I was struck with how directly buyers would seem to attack my pitch. In other countries I would show a slide, ask "what do you think," and my conversation partner would answer with "looks good" or some other affirmation. In Germany, I seemed to be challenged directly - I felt like the pitch wasn't landing.
Germans are generally deductive thinkers. This means they don't just want to understand the basic output of your product and the results they might expect working with you, they want to know the How and the Why behind it. Combined with German directness, this means challenging can often be a positive - a desire to understand more signals interest.