Unless it's hard-to-find I don't tend to buy books on Amazon but I do use it a lot for music - there's no independent retailer in Plymouth that specialises in what I listen to (and about two overall), HMV is awful and they have a lot of stuff on the MP3 store that's otherwise out-of-print (most of the Sarah Records output is on there for example). I try to buy as much as possible from Spillers when I'm in Cardiff but, again, Amazon really is very cheap and very convenient. I think it's even worse with bookshops though, I can't find a decent independent bookshop for love or money and even second-hand ones that aren't charity shops are getting rarer and rarer. Waterstone's having destroyed almost all its competition it's gotten gradually more dreadful, and with no real alternative (on the high street at least) it can get away with it.
Ask an Amazon supplier what they think of them:
"Yes, we'll stock your books, We want 60% discount and you'll have to pay for anything you send that doesn't arrive in perfect condition, or we can't shift. And we want FoC copies for publicity purposes"
"Make that 62% if you want the same payment date. Otherwise add another thirty days."
"No, we didn't tell you we'd changed our payment procedure. Send us another load of invoices and they'll go to the back of the queue."