Amazon provides a Look Inside feature. Many customers use it before deciding to buy or to choose another title in preference to yours. The first chapter should be so good that no one walks away at this point!
In the argument about whether to place glossaries and such like at the front or the back of the book, I suggest it might be wise to let the customer get at the first chapter without distraction. Other Book titles, glossaries and possibly even maps, should go at the back where they don’t get in the way of this first, all-important read.
The opening line of the chapter is like the first line of your blurb. It should arouse curiosity and engage interest, needs to be so good that the customer will decide right away to buy.
Like the title and cover, the first lines must reassure that the customer is in the right place; that the genre is the one he thought it was and likes to read. Check your first lines and remove anything that might prevent a sale. This is not the place for back story, poor spelling, stilted language, or poor formatting. Concentrate on the things that will help the reader make a good decision – suspense, curiosity, personality, language that flows smoothly, ideas that link to one another without a distracting jerk. Take time to get it right.