It depends. There are those that grab up cheap stuff and such, taking things from regular collectors, and then jack up the costs and don't do deals. I know one or two of those in the area. On the other hand, I know some other guys who are pretty cool, might still grab things collector's might want, but can do good deals or do well enough in trade.
I remember this one flea market seller that had a busted Jungle Green N64 controller. The analog was trashed and it was dirty, but at the time I had some spare N64 controller parts, so I asked 10 bucks for it, because it is a busted controller, and she told me no deal. She had that thing up on that wall for years I think. I don't know what she was selling it for exactly. I wonder how they stay in business...and some don't as she eventually shut down because I'm pretty positive she was never willing to negotiate things in a market that could be very fluid at times. These people drive me nuts, because I can't imagine they are making the money they could if they just lowered the price even abit on things. Why not sell for 40 bucks if you don't ever sell for 50 or 60?