I don't think anyone has addressed this. It's not haggling per se that's annoying, it's playing one dealer off another that's annoying. If someone wants to make an offer that's less, that's one thing, but to say "Billy Bob Rabbit Thumper down the road will sell it for x, will you sell it for y is just annoying." What that tells the dealer right off is that the dude is going around wasting people's time and is not interested in making an honest deal. There is much talk of dealers being rude, but customers acting in this fashion is every bit as rude, probably more so.
I agree. If you want to be treated well, treat others well, and that includes those with whom you do business, both as a buyer and a seller. Many people make a game of hammering out the last nickel on a deal, and they have no regard for those with whom they are dealing; it's all about getting as much as they can, and they are obsessed with gaining the greatest advantage over others.
What amazes me is the amount of time and energy they spend going all around playing one guy off against the other. If they save $50.00, but spend six hours and five gallons of fuel, where is the advantage in that? My time is worth more than that. Nobody gains, everybody loses in a scenario such as that. Sane stewardship of one's financial resources is one thing, but it's not that.