I kind of agree with Twinfan here.
I also feel your pain, but whether we like it or not, the interweb thing is gradually turning us all into traders :(
I'd rather be able to walk into a shop, look at the price tag, decide whether it's worth it to me (this is guitars, shoes, jackets, boxes of eggs, whatever) and make a decision based on the asking price. I don't want any of this haggling sh1t, or feeling like a numpty when I've bought something for X and someone tells me "didn't you get a discount? take it back, you could've had for Y if you'd etc, etc..."
But that's just my cultural preference I spose, what I grew up with... If shop A's prices for butter are too high, go to shop B...
Nowadays you can probably do a deal on anything (I wonder if you could cut a deal on the checkouts at Sainsburies?? :lol:).
In your situation, the bloke paid something for it, which he presumably thought was fair, he has to make a buck, he's asking what he think he can get for it... and you got to remember, if he's running a shop, he is a trader :lol:
People buying concert/sport tickets to make a buck selling above face value still p1sses me off, but this situation I can't really argue with - there's an object for sale, which seems to be in demand, he makes a living buying and selling objects like that, you're a buyer... if you don't like the price, you can wait for a cheaper one (or track down the cheaper one on the net, or go to the US to get, etc, etc). If he's got it wrong, he will have to drop his price to shift it... If someone buys it at his price, he was right - and that is what the guitar was worth... (might not be when the numpty's walked out the shop, but that's the next link in the chain :lol:)
Still feel your pain though :(