[WhiteDay]

こんばんわ!

I wanna know why they use different words (は and で) in these two sentences: (from Minna no nihongo 2)

-IMC は 何を つくって いますか. (IMC wa nani o tsukutte imasuka - What does IMC manufacture?)
-あの みせで なにを うって いますか. (ano mise de nani o utte imasuka - What does that store sell?)

Like why don't you put で in the first sentence or put は in the second one? Or even why don't they use に in both? To me they mean quite the same. So what's the difference?

Thanks a lot.