I'm a student who works 9 hours a week at Animates. I appreciate your sweeping generalization, but not all sales people are like this. Personally, I give people advice to the best of my knowledge (and I do consider myself an expert on all of the fish & products we sell) even when that means saying they can get something cheaper elsewhere, or telling them they don't need the product they're looking at. We don't work on commission.
All I say to most people who wander into the fish section is "Are you okay there?" half the time the person will say yes and I'll walk away, but the other half they'll have a question about a product, fish, or some problem they're having with their tank. We can't read people's minds, the only way for us to know if they need help is to ask them. A lot of the time I'll be so busy they won't have a chance to approach me themselves, and in my experience a lot of people aren't forward enough to go out of their way to bother a salesperson.