Buy сologne at or in perfumer's
Buy goldfish at or in pet shop
Buy drug at or in pharmacist
It is possible to use either 'at' or 'in' with places where you buy things.
Do make sure that you use articles correctly, though. Remember that a single countable noun always needs an article. Here are some examples:
Buy a goldfish at a pet shop.
Buy some drugs at a pharmacy.
Thank you very much for your comment. I am never sure about articles. There are my Achilles heel. :D
at the supermarquet
hi¡¡ I think that we buy bread in a bakery. hahha but I'm not completely sure...