That's really an issue: if you aren't the hard-boiled, super unemphatic negotiator type you'll likely buy the very first thing a salesperson has invested face-minutes in, if it just gets the easy 80% of requirements/desires right. "Thanks for your time, but I'll go see if there's another offer that is maybe 3% better or 2% cheaper" isn't something that feels good to all people. The asynchronous experience of online shopping (and before that: mailorder) is a huge enabler to people who aren't the haggler type. And because the haggling mindset is a learned skill, I'm afraid that it will only get worse the less people grow up shopping face to face. To future generations, every shopping experience that isn't online or at least highly formulaic self-service like in a supermarket will feel like the haggle scene from Life Of Brian (and just as alien as the one after that).
But obviously a total amazonisation of all buying would be terrible nonetheless. What I'd love to see: a site like those price comparison directories but not so much focused on cheapest but on local availability. Current stock, proximity, opening hours and price, they are all important.
Actually I should have gotten my ass up and looked for funding years ago, or at least part-timing it on the side (I'm not the haggle type, right?). It would all hinge of course on integration interfaces with whatever systems local dealers already use for managing stock, because those claims world need to be reliable or else it would all be futile.