I've collected comic books for over fifteen years and I have found through my experience that Overstreet's Price Guide serves the purpose of grading comics best. One the opening articles of the guide is decicated to grading comics. This includes grading terminology with a succinct description of each major grade(Near Mint, Very Fine, etc.), factors that will influence the price of a comic(for example, high-grade comics will generally be sold for 50% to 100% over the listed guide price), tips on how to put a collection together as well as sell a collection ( for instance, the guide indicated which category of books would need to be listed individually when selling to a dealer), and a report of some of the top comic book sales of the previous year, plus much more. In my opinion, these opening articles embody the fundamentals of comic book collecting and are required reading for anyone seriously entering the hobby. The Overstreet Guide is also more thoroughly illustrated with black and white photos of comic covers than any other guide I've seen.
Whether I've bought or sold books (I'm not a professional dealer, by the way, I simply sell books from my collection from time to time to generate cash for a new comic I really want) I've always found that the prices and particularly the grading standards listed in the Overstreet Guide are what is almost universally excepted by collector and dealer alike.
I've consistently found the listings in the guide to be thorough and complete. Overstreet makes a concerted effort to indicated which issues have artists and key events that many collectors are looking for(An example would be: N.Adams art, 1st appearance Ras Al Gul). Of course, everyone has their own opinion of which issues are most important, but Overstreet does a fine job of listing the ones that most people demand, and there are many. A previouse review indicated that the Platinum Age listings may be incomplete. However, I believe there is an article preceeding this listing that indicates that, because material from this period is so rare, the listing is more than likely incomplete. Additionally, the author invites any collectors who have issues from this period that are not included in the listing to contact the author so that the new information can be incorporated into the new edition. Another reviewer felt that the listing for Modern Age comics was also lacking. There may be two reasons for this. First, the edition you purchase takes several months to prepare, and when it is published, it represents the activity in the comic book market for the previous year. The Modern Age issues in question may have been published durning the period of time that the guide does not cover. Second, the comics produced in the last ten years, with a few exceptions, represent, in my experience, a very glutted market. Supply of these books far surpasses demand. Thus, most of these books don't experience much of a price increase. So it's possible that a book published within the last couple of years that hasn't increased above its cover price in value may not be included in the guide. What would be the point? And in either case, these issues will more than likely be included in a future edition.
As regards the claim that Mr. Overstreet "fixes" the prices in the guide to suit his personal interests, who can really say? What can be said is this: only a person who has a thorough knowledge of and an avid interest in the medium (i.e. a collector) could produce a comprehensive grading and price guide for the use of other collectors. I can't imagine a guide put together by someone who had absolutely no interest in the hobby. Where whould such a person get his information from? He'ld have to depend on other collectors and thus you'ld more than likely have the same charge of conspiracy all over again. Mr. Overstreet evidently has not only the the knowledge and interest but the experience as well as the knowledge and experience of his many adivsors. He's just as qualified, if not more so, than anyone else.
Let me provide a word of caution. The Overstreet Guide contains numerous dealer advertisements. Some are genuinely strict graders and provide excellent products and service (Four Color Comics and Metropolis Comics are two of these). However, there are many who are VERY liberal in their grading and whose claim of "unconditional money back guarantee" quickly evaporates when you try and make a return (Want List Comics comes to mind). Buy all means, take advantage of these dealer listings, but do so with carefully.
To conclude, I sincerely feel the Overstreet Comic Book Price Guide is the best available. If your serious about collecting comics, it's a valuable tool for buying, selling, and personal research. I've learned much from just going through the guide page by page and discovering books I never thought existed. Additionally, it's more than likely that at some point in your collecting you'll have to deal with someone who uses this guide a the standard.