Don't understand how haggling over a pint has got any similarity to trying to get the best value for money on a contract.
I don't haggle in the pub. There would be little point in haggling over a pint. The price is set by the establishment and the bar tender has no say over it. If I want cheaper I'll go to a different pub (if I have the choice).
Haggling over a contract for work however is in my mind perfectly acceptable. In fact I expect most quotes to have included a fair mark up which they are willing to cut. Just the same as buying any service you pay the price your happy with.
Recent real life experience is having double glazing quotes exceeding £8k and eventually agreeing a contract for £3.4k. I'm very happy with the work. If I hadn't haggled it would have cost me much more.

