I moved to Berlin recently and have been trying my best effort to improve my German and speak it in…read moreshops, etc. However, (what seemed like) the owner had no patience for my broken German and so we switched to English. He was still irritated, berating me that English is not his first language. I was looking for advice on my bike and possibly a tube replacement, he did not seem interested in doing so. I started to leave the shop and he shouted at me to come back. It got to the point that I was almost in tears in this man's bike shop. If you are able to speak fluent German I'm sure your experience will be smooth, however I would not recommend for those trying to learn German.
Edit: After returning to collect my bike the same man told me he never wants to see me again, I responded with only politeness, but he will definitely not see me again. Kindness is important.