I am not saying the Comic Price guide model is dead, I am saying it is on life support. Currently, there are no monthly comic book price guides (think Wizard Magazine) that accurately track prices. The big books come out every year, but they do not capture the prices of books that spike before or after the publication of the book. If a book starts spiking on eBay before the book is published, it will not be captured until the next edition. Basically, if you are looking for newer hot books, the price guide model is dead. If you are looking for older books, it still might not be helpful.
Think for example Invincible Iron Man #55, the first appearance of Thanos, sure the price guide shows a value for the book and can tell you that it is his first appearance, but the price guide cannot keep up with the trends (in this case Thanos being in the Avengers Movie, or appearing in the Guardians of the Galaxy Movie) and therefore, cannot keep up with the rising price of the book. I don’t know about you, but I cannot wait a full year to find out the current value of a book when I go to sell it.
So what is one to do if the price guide model is failing? I like to check out online guides such as Comicspriceguide.com or Comicbookrealm.com (my personal favorite of the two.) These two pay attention to what is happening on the eBay market place and update the prices quickly. People can also submit closed auctions to show what books are actually going for.
Comicbookrealm.com also allows you to use their database to track your collection, which I find better than doing my old spread sheets. (It is free by the way.)
While these two price guides are not “official” as per the Overstreet crowd, they are helpful in looking for what is trending and what books are rising in price.