"I was inderectly refering to the Quaker invention of honest pricing. If the price on the tag is £1, then it's £1, if you don't want to pay £1, go somewhere else. If the price on the tag is £1 but I'm willing to accept 50p, then that means I've been lying to you."
Because price is not an absolute. Perhaps a minimum, certainly for goods, but this is a discussion of services.
It's like my labour cost. If I'm asked to quote for some work, I'll give an honest rate. So normal rate if I don't have anything on, and a cancellation rate if I'm bumping something else. It's considered unprofessional, even discriminatory, to not quote someone. So I won't say "no, I'm busy" rather "give me two thousand on top of my usual fee and I'll do it".
I consider it fair that I only ask for parts cost from my friends, family, neighbours, mechanic, plumber et al, but that I'll charge Jo Public for the same pleasure. Hell, not even parts for a plumber* who will actually show up on a Sunday.
Even with basic mercantilism (buy for a buck, sell for two) there may be times when you need the cashflow more than profits, so selling twenty items for $30 is more useful to the seller than the "honest" price of $40.
As for lying, does that apply in the other direction? I often buy things to resell, people want quick cash rather than maximum value, so take less money than the items are worth.
I guess I'm slightly dishonest when going someplace that I'll be haggling. No suit, paintballing hoody, beat to shit backpack etc.
Oh, and bear in mind that for many places you're haggling, the thing you're buying is not actually the product the salesman is flinging. For cars and some degree property, the loan is where everyone makes money, not the goods.
How to determine the correct price of something is a fascinating study in microeconomics. The best answer still is "what ever the parties decide"