"Butikken sælger de fleste biler."
Translation:The shop sells most cars.
I assume this means 'more cars than other shops', rather than most kinds of car, which is what 'The shop sells most cars' implies in English.
I interpret it as a shop that sells most kinds of cars.
"The shop sells more cars (than other shops)" is "butikken sælger flere biler".
"This shop sells the most cars" is "denne butik sælger flest biler".