Buying shoes for running (and cycling) is somewhat technical, more for running, in my opinion. I would not go to a big box sporting goods store.... as you said, they often know nothing.
And, if you are cycling on flat pedals, in running shoes, please, please find some shoes with a stiff bottom. Some people buy a pair of mountain bike shoes and don't install the cleats, but using a pair of light hiking shoes often do as well. If you are riding in sneakers, the sole is too flexible and eventually, you'll be dealing with foot pain.