Edit: Just tried Fire Emblem Shadow Dragon with a save I found on gamefaqs and everything worked. That is battles AND shop. Tried on both DS and Desmume.
Whenever I try to connect to the wifi shop in Fire Emblem 11, I get error code 20100 which means that the device cannot connect to a network. However, when I go into the wifi settings and test my connection, it comes up green. I'm not sure what the cause of the problem is. I'm using the emulator Desmume and my connection to the internet is wired if that helps.