We choose to sell the best quality products available , whether it's something simple, like granulated chlorine shock, or something more esoteric like an o-ring for an old filter. You can always find something cheaper at a big-box store or on the internet, but is it the quality you need and who do you ask? Take algaecide, for instance. Most algaecides you can buy at a big-box or hardware store are half-strength and/or based on ammonia. Nobody there can tell you that It won't do a good job killing your algae, and it will foam up your pool for a week. That's not a problem you need when you're trying to get rid of algae.