I'm not sure why you've had so much trouble, but I can't say I've had the same experience. Well, I did have an issue with a vendor who is no longer a member here. Other than that, I've always head back from them.
Sometimes these guys are really swamped, and just like everyone else, some things just slip their mind. I generally try to give them a few days to get back to me, and if I haven't heard back from them, I'll send them a friendly reminder.
As a rule, I think it's safe to say that some vendors (not just here) would rather not deal with "price shoppers". Many of them have a steady flow of in-store customers to keep them busy and financially stable enough that the few sales they may lose from price shoppers is not a real big deal to them or their bottom line.
If you haven't already, I'd try the friendly reminder route. At least give it a shot before giving up on local dealers. There are many positives to buying locally if at all possible.