Not many people here will give you any kind of hard time for feeding live, it's a pretty common practice. I think the store clerk was being a brat for one, and I have never heard of snake killing antibiotics for rats. Probably wouldn't have risked it, though.
I used to go to petco when I needed live feeders, since that company is much more accepting of the concept of rodents as food and the employees are less judgey at you for it. Also, Petsmart rats are stupid overprice and GIANT, which I think is because they're usually retired breeders.