All the time. Rarely do I go into a pet store without someone asking me for advice. The other day I was at the local pet-smart getting a batch of ghost shrimp when the people at the check out started asking the cashier about the betta they were buying and care. The lady looked a bit clueless so I stepped in. The guy though he could just dump the betta straight into the tank and I explained that you have to let the fish adjust to the temp first by floating the fish. I had to repeat this several times because at first the guy didn't quite understand.
I've been randomly stopped for advice though at every pet store save one that I've been to and helped people with everything from plant selection, fertilizer questions, and fish care/requirements/needs. It's nice though to be able to help people make better choices.