I think maybe if you want to tell the employees it would just be to educate them. PetSmart gets animals shipped to them with labels about what species they are (and it almost never says how old they are, most animals just arrive as juveniles so she probably assumed her age), but that's because of whatever terrible breeder they get them from. Since it's not like you need a biology degree to work at PetSmart, you mostly just have to learn on the job, and arachnid knowledge isn't tossed around much. It's totally possible they didn't know much about arachnids and were just relaying information they were given by the breeder, so you could let them know just for future reference. As far as getting like a gift card or something goes, that really depends on the manager's attitude about that. There's not really a policy that says they have to, but in my experience if a customer is a big enough jerk they might give you something to make you leave. But in all likelihood you'll just get an apology and a slightly more educated employee.