Plenty of jerks in any hobby. Sellers, buyers, it goes both ways. I must say, though, after 10+ years in pinball, the list of lifelong friends is MUCH much longer than the list of 'people I'd cross the street to avoid, if I were walking down the sidewalk and saw them coming'.
As a buyer on a pinball forum, you always want the best price. As a seller, you have to make money to survive. Making money isn't necessarily evil. Trying to negotiate the best deal isn't always evil.
You know when you go to look at any pin that a sale/deal is not guaranteed. That's why you're going out to look at it. As LTG says, no deal is better than a bad deal!
I've walked away from a transaction where the seller had an unrealistic price in mind, handed the seller my business card with a number written on it, and said 'The game is worth $x to me, please call me if you get to the point you will take $x', and gotten calls back.
I've had sellers not understand what was required to bring the game back into shape before. Some think I'm lying to them. Some believe me.
Just because the guy has a price he put on the item that seems unrealistic to you, or the condition doesn't match what you describe, doesn't make the guy a bad guy. Maybe it's worth that price to him, he will keep it if he doesn't get X. That's OK.
Treat people how you'd like to be treated, whether you are buying or selling, and you'll have better luck. If a deal doesn't work out, there's always the next.
It's only pinball.