I like to support local small businesses that I know and trust. Would you rather buy the exact same used car from a relative/friend or some stranger in the classifies who is selling it for a few hundred dollars less? Me?, I'd rather help out a friend.
I buy most of my chems at my dealer. I like to keep in touch. They know me when I walk in and we get a chance to talk spas. I like to use non buffered MPS and my dealer sells only buffered, so I get this elsewhere...and to be honest for a whole lot less money..but I still like to support the dealer.
I also have a pool so I get to pool suppliers once in a while. Most of them carry spa products and I have noticed you can purchase some of these products for really small dollars.