What all is considered when determining how much something is priced in the guide?
For example, I noticed in the online guide that Iron Soldier III for NUON is priced at $30, while Spider-Man: Web of Fire for 32X is priced at a whopping $80. This seems inconsistent to me because Spidey is only a R7, versus a R6 for Iron Soldier III (and I was under the impression that both had similar manufacturing numbers). The popularity of the Spidey franchise could play a part, but in eBay auctions I've seen both go for around $80 complete. I realize eBay isn't often a good judge of a game's "true" worth, but it certainly has to be considered as part of the equation and it would seem like it has been in Spider-Man's case. I don't doubt that Spider-Man is worth more than Iron Soldier III, but in this scenario (with the rarity being roughly the same and online auctions yielding similar results) I don't see how Spider-Man could be 166% more valuable.
I'm not trying to say the pricing is inaccurate, just looking for a clarification on what all goes into the decision-making process that would explain such an apparent difference in similar games.
And yes, I do have a vested interest in the answer to this question...can you guess which of the above games I own? :P