There are many book sellers around. But, straight to the point, what we all are looking for is the best deals around; the person who sells the cheapest with the best quality. For book buyers, we all know that what we are looking for is for the book to be in good condition. Especially when buying used books, any writings are missing pages in it is a definite no no.
When buying books online, it is best to buy from reputable book sellers. In this way, you can almost ensure that the book you buy will satisfy your demands. I can't really recommend any online book stores for you but if you are really desperate, click on the links on the left and it will direct you to some bookstores specializing in best sellers and textbooks, just to name a few.
However, I would suggest that you go online to find your books rather than any other book stores or 2nd-hand bookshops. There are some advangtages to this, mainly that online, books are usually cheaper, a main factor among buyers. In addition to that, the condition of that book is usually quite good too. Thus, online book stores are sprouting out and it has become immensely popular.