Criteria used to rate a book.
1. Security - getting paid is by far most important.
2. Working with the forum. This is a player's thread and books are held responsible for their actions. Questions are asked of books concerning number of employees, time in business, experience, poster problems, etc. If a book is going to ignore a player's thread, they will be severely downgraded. Most books are very easy to work with. There is one book that still hasn't replied concerning a problem with a player. If there isn't a reply, this is going to hurt the book. That said, this thread isn't going to used for arbitration since it's a no win situation.
The following cannot be quantified as to importance since being highly detrimental in one category may supersede other criteria used.
3. Poster review - poster review is much more important at bitcointalk than other forums, but other forums are also read. A high review from a new book will weigh less than the review of a book that's been in existence 2+ years.
4. Anonymous - one of the reasons that bitcoin books are used is to stay anonymous. There may be times where it is necessary to question players but it should be a minimum.
5. Margins - If players are going to have a chance to beat a book the margins have to be tight enough to give us that chance. If the margins are larger than -110 (1.91) that's a big blow to a book's rating.
6. Payout speed - If the average is longer than one hour, a book will be downgraded. One hour is sufficient due to possible grading errors. A large book is dealing with a significant amount of money along with a huge player base.
7. Markets - The more betting options, the better.
8. Traffic - time in business along with amount of players that a book has gives us a large sample size.
9. Currencies used - It's easier on the player if we are allowed to deposit and withdraw from alts.
Miscellaneous - Books accepting fiat currencies are omitted from the guide. Other forums are read to make sure the ratings here aren't significantly out of line with the average of other books.
https://bitcointalk.org/index.php?topic=717790.0
