"Are they selling it anywhere?"
Translation:Prodávají to někde?
I answered: "Někde to prodávají?" and it was marked wrong. Is this not an acceptable word order?
It is correct a correct Czech sentence. Possibly a slightly different meaning than the default translation. I am not that good in English to know all the nuances of the English original, but it might cover both.
Your word order would be used, for example, when you were surprised, so you repeat the previous declaration with a question.