If you're talking about a retail shop, and they're a good, reputable retail shop, then their prices are always going to be higher ... however, you'll usually get support in the form of a warranty from that retail shop (they back up the work they do refurbishing their game) ... that's invaluable if you're new to pins and don't know anything about them. I doubt their money is going to a boat payment . Unless boating is in your blood, a good businessman knows that the day you buy a boat and the day you sell a boat are the happiest days of your life (there are a couple of pins that fall into this category ... Orbitor 1 comes to mind ).
If you are talking about a Joe Schmoe that tries to sell a horrible condition Gold Wings for $2K, chances are that money is going to a meth addiction and not a boat payment . Seriously though, some people see "pinball", look on ebay, and put their crummy game up on Craigslist for insanity money. Just ignore them. I bring up Gold Wings since it looks like a high end pin . I get a kick out of it, but it's a $500 pin no matter what the market says .
In this hobby, you have to network. You'll eventually find acceptable prices.