Quoted from sbmania:

Bob and Guido above have it right. I've been attending shows for over 30 years. Set up at the very first Allentown show when it was at the firehouse and pretty much every one since then. Set up at many many York shows over the years. Before all that, I attended many of the huge gameroom shows at Hackensack, Valley Forge, and Chicago, buying, selling and trading.
Since the Roman Chariot days and before, people have always bought things in rough shape, fixed them up, and tried to sell them for a little more. Houses, cars, furniture, antiques and yes, even pinballs. Nothing has ever been wrong about that. Its fundamental capitalism. Which of you who have owned more than one house sold your last house for the same or less than you bought it? I'm not sure where the line is between being a "flipper" and being a hobbyist who like playing and fixing pinballs. But as far as flippers being leaches, giving nothing back to the hobby, etc, that's crap!
If people who pay to set up at a show can't make a little money, guess what. Pretty soon, they don't come back to the show and there is no show. I have bought broken down games over the years, fixed them up, and sold them, either at a show or privately, to some homeowner who has no idea of how to repair his own machine and except for me and others like me, would probably never have had an opportunity to own a pinball machine. But because I fixed one up and sold it to him, he plays it, his wife and kids play it, their friends and neighbors play it, and next thing you know, somebody else is looking to buy a machine.
Then I tell them or they hear about the local shows coming up, they come, pay their entrance fee, and spend money with the various vendors. That's how shows get built.
As far as making money doing this, I don't think anybody is getting rich in the process. At best, you hope to make a few bucks which inevitably goes back into the hobby buying parts or other machines to fix and play. My time is worth just as much as everyone else's time, and I don't plan to spend hours and hours for nothing, just so someone can benefit from all of my labor while they did nothing. That's just the way it is. That doesn't mean I don't do favors for people from time to time. I have spent hours helping friends fix their machine with nothing more than a thanks at the end. I have bought numerous games and "flipped" them to friends for exactly what I paid, because I knew they loved it more than me and wanted to have it. I have given newbies parts and advice for free, just because I thought they needed a break and a bit of a helping hand to get them started on their pinball journey. But if I buy a game, fix it up, bring it back from the dead, and make it look as close to new as possible, I want some compensation for the dollars and hours upon hours of labor I put in. That's not wrong.