It is a lack of supply and an increase in demand. If it was just flippers then they wouldn't be selling so fast or easily. I don't disagree that $400+ is a very high price, but the market seems to be bearing it. Whether or not it will last is anybody's guess.
We've seen regular proof that flippers are manipulating the market. We're not joking when we talk about a recently sold game reappearing on eBay for double in a couple weeks. We have watched it happen time and time again, and repeated by the same people again and again. Too often the same seller or proven aliases buy up literally every copy of a game which appears on eBay near or below what they sell it for. Many brag about how tall their stacks of Magical Chase are and after a new ceiling-raising sale (or appearance of), too often several copies of a supposedly rare game suddenly flood the market.
Personally I think it has less to do with "uneducated" buyers and is more so a sign that people are simply willing to pay more. I think part of this is an increase in buying power as more people in my generation ascend financially. It certainly is in my case. I admit that I paid $400 for my copy, and I would do it again. (Allow me to now duck, to avoid flying objects being hurled at me.) I can afford it, so why not? I would have rather paid less, but at some point I just accepted it. Some of you probably think that is bad for the market, but I just wanted the game. I would rather have Beyond Shadowgate than $400. /shrug
We get too many uneducated buyers flooding this forum alone, asking us what to pay for games they aren't familiar with, let alone the set collectors on various forum openly talking about putting together a quick and easy TG-16 "set". They often cry about how they lost out on their third attempt to pay an outrageous price for a particular game that is always available for a fraction of those prices.
We also get too many people here trying to get a high return on their "investments", who call us a bunch of liars and scammers for pointing out with links all of the recent sales which went for half of what they paid.
That's the worst part of all. So many nu-collectors openly talk about how much they hate the TG-16 and its library and know nothing about the games they will or have already paid anything for. What's left of the natural market on the side for actual Turbo fans is a fraction of what exists.
No one ever suggested that the entire Turbo market is resellers and uneducated buyers. They are just the ones mostly responsible for the two tier market. If it was simply game lovers having so much buying power, then why would any of them ever part with their games if the money isn't a big deal?