I didn't question the trope of magic item shops back in the 1E/2E days. I wouldn't run it that way now. For anything more wondrous than healing potions and +1 weapons/armor, the characters have to network through patrons, quest givers, guildmasters, mentors.
This isn't a big problem in less experienced/more casual groups, but some players (myself included) do like to pore over articles like "most powerful wondrous items for bards". I don't think it's good for the game to feed an expectation that characters can acquire any item they can name if they just save up enough coin and search enough magic shops.