Translation:Many sales clerks are shouting at the market.
Because Hungarian! ;-)
It just a subtle difference between the languages. Places which tend to be "open", flat areas - a market, the airport, the railway station, we would certainly never say "on" the market/airport/railway station, but "in" or "at". The Hungarian mind thinks of it as "on". We simply have to adjust, just as Hungarians have to do so the other way when learning English.
Thanks for that explanation. I think while there may be some inconsistencies in the course, the important thing to understand is that sometimes the preposition used in Hungarian and the one used in English are different because the concept is being thought through differently. Anytime you translate languages you must realize that you have to translate ideas, not just words. I like seeing the literal translation so I can understand the Hungarian thought process, but then I also like seeing the more natural English translation so I know the English equivalent.