I think EVERYONE pays too much for their first pinball purchase until they learn the ropes. It pays to shop around and ask plenty of questions on our great forum. I'd say it has saved many newbies from over paying for their first game.
I guess you "know you have overpaid", when you see a better game for less than you paid. Happens all time. That's why you shop around, and NEVER, EVER restrict yourself to eBay or dealers. Private sellers can give you the best deal.
There is always an exception to the rule....in this case its my first machine.
I paid $40 for a Flash, and thanks to the help on this forum had it going in 24 hrs!!!
As others have said, best to ask plenty of questions to both the seller and guys on the forum
