joethomas, that's an excellent question.
I often buy textbooks online (just 3 this past week, and one just
arrived by DHL a few minutes ago...), so I am quite knowledgeable in
this specific area.
The first place to go is Glenn Fleischmann's http://isbn.nu - this is
absolutely the #1 book price comparison site, and you will be able to
quickly locate the most inexpensive options. Glenn's site also allows
you to calculate prices with shipping and taxes added, so you can
receive a true comparison.
If you are buying your textbook new, you're done - use isbn.nu to
locate the most inexpensive option, purchase it from that site and
wait for the textbook to arrive (note - over the past seven years,
I've purchased hundreds of books and CDs online, and only a couple
failed to arrive, so in general I would not worry. One thing to look
out for is that when you submit your credit card information the site
you are working with support secure socket layer or SSL - you can
easily verify this by checking that the site address is prefixed by
"https://" rather than by "http://")
If you are buying used, typically I only purchased from Amazon or half.com.
In any event check the feedback on the seller - it's worthwhile to pay
a couple of dollars more but to purchase from a seller who has a very
high feedback rating and has completed many transactions; this all
goes to increase the probability of a successful transaction.
For example, on Amazon - say you're shopping for Kotler's Marketing Management:
Book lists for $126.67, but used books start at $44.99
If you look through the various options, you will see that most
feedback ratings in this case are quite low (4.1 seems to be common /
5.0 is the max) and that many of these sellers are either new or have
completed but a handful of transactions.
In this case I would likely purchase from Sene for $59.95; Sene has a
rating of 4.5 and has completed more than 700 transactions. You may
also want to click through and check what buyers are saying about this
Before completing such a purchase, you'd do well to see what half.com is offering:
You can find this same book here:
You'll immediately see that the same book is offered for less and from
more reputable sellers, but you'll want to carefully read what you are
getting - e.g. a softcover edition, international edition, if includes
CD or not etc. You can contact the sellers with questions on both of
these sites prior to completing a transaction.
Please do let me know if this is satisfactory - and ask additional
questions if you feel I have not addressed all of your concerns.