Whenever I come across a customer who want to put an oscar in 10g, or wants to use the cheapest filter for his goldfish tank, I tell them this:
"Imagine being locked inside your house...no air is coming in or out, and the garbage is never taken out...oh yeah, and there's no plumbing. Imagine what life will be like after a week in that house. Then imagine sharing that same house with several other people. Things are going to get pretty nasty pretty quickly..."
I explain to the customer that filtration is the aquarium equivalent to indoor plumbing, and then ask what quality septic tank they have. Soon I probably ask them that if they were a fish living in their aquarium, would they prefer the cheapest filter or the best one.
Water changes I often liken to regular household chores, like taking out garbage, sweeping, mopping, dusting, doing dishes, etc. Could we live in such an environment for a month or so? Sure, but it would get icky fast.
I've been using this analogy for a couple weeks now, and for the most part, my customers seem to be making better choices for their pets...not to mention, they're buying more stuff; too bad I don't get commission). For those of you who work in petstores, perhaps giving this perspective to customers might come in handy, and you might feel a little happy when you clock out, too.