Kind of unrelated, but I work in a women's fashion store and I could never sell clothing to someone when they don't need them or aren't sure, rather then letting them spontaneously buy it and regretting it later. And I'm happy to tell a customer that something doesn't suit them and point them in the right direction, without embarrassing them or insulting them of course. Up selling is one thing, but pressuring them is another thing, and will make the customer too uncomfortable to return unless they're 110% happy.
As for pet shops, they get a bad wrap don't they. I don't usually talk to staff because I usually go into the pet shop knowing what I want or to compare prices. But I'll never forget the time, that the pet store we used to buy frozen rats from (the manager was supposedly a 'friend' of my mums), did not notify us that their freezer had failed and instead of disposing of the thawed animals, had refrozen them. Which killed my first ever snake, which I got when I was nine. Devastated. I only hope that that particular pet shop goes out of business soon anyway, and make way for the good ones that are around. Upside of the story is, I ask a billion questions before I buy frozen rats now, and if they can't answer them, the snakes wait another week.