Okay, I will be a bit of a contrarian. :)
Here are things that will make me avoid a cookbook unless I hear a good review from a source I trust:
1. There are too many pictures. I buy cookbooks to learn recipes and cuisines. More pictures means less learning. The exception is pictures that illustrate techniques. A few pictures of finished dishes are okay, but landscapes, market pictures, pictures of the author, etc. are no-nos for me.
2. The author is a celebrity who has no training in the culinary arts and has never worked with food for a living, e.g. cooked or run a restaurant.
3. The recipes are more appropriate for a restaurant setting than a home setting. For example, they may require you to execute multiple sub-recipes whose yields are much larger than needed for the recipe you are executing.
4. The recipes are too detailed. A few in-depth examples are fine, to illustrate a technique or class of recipe that may be unfamiliar to many readers. Of course I am not objecting to people writing cookbooks aimed at beginners. It is how we all start out and they are a good choice for some. On the other hand, as an experienced cook I find it easier and more pleasant to follow a recipe that is clear and to the point.
5. The recipes are hard to read. Tiny print, light-colored print, and page breaks that make you turn a page are sins.
6. The recipes are simplified but portrayed as being authentic. I have no problem with simplifed versions of recipes or Americanized versions of ethnic cuisines - after all, the results can still be tasty and sometimes that is exactly what you want. I just want "truth in labeling".
7. The book is a rehash of recipes from the same source that have previously been published. An annual volume of recipes from a magazine is okay; a book full of the umpteenth versions of basically the same recipes by the same author/source is not.