I've been screwed on deals like this --- twice -- in Allentown deals. On the last one, the seller had swapped boards and installed inoperable water damaged boards. Of course, I didn't check because of photos and video shared in the days prior showed no reason to do so.
It sucks. "You" want to trust people... but at the end of the day, you should only buy a game that can be seen and inspected in person. And even in those scenarios, don't stand in front of the game and ask questions. Dig into the game yourself.
People can and will actively pull a fast one on you if you let them. Not everyone, of course, but when it comes to money and fast transactions, it can happen very easily...
Ask around enough and you'll find some names frequently coming up (names that you constantly see here on Pinside). I know of three right in the MidAtlantic (two in PA and one in VA) that are always on Pinside selling games... and I could link you with multiple people that have all had issues of honesty with them.
Sorry that happened to you @knockerlover. Lesson learned