I've lived in Germany for about 8 years, mostly in Frankfurt and I can say that locals are indeed very friendly, but I've encountered some that are tricky to deal with. For doing business, Frankfurt could indeed be tricky. Some people here seem to look into the smallest detail and generally feels tense as I have to calculate my every possible step to avoid getting myself in a situation where the other party finding something fairly insignificant to bother me with. Nice people I've encountered pretty much everywhere in Germany, which is amazing. The nicest, probably in Cologne, very relaxing to do business with, kind, friendly and flexible. Bavaria is a mixed bag - from the greatest experiences with Germans ever in Munich to inflexible in Nuremberg especially, Bamberg and close to the Austrian border and on the opposite in Salzburg, Austria. Essen, Dortmund are not the friendliest, nor most flexible. Berlin - always good experiences, not great, but good.