There are many booksellers trade associations around the world. Make sure you save all email regarding the purchase until you know you're satisfied. Create a special folder in your email program to store all your book purchase messages. That way you can go back through them if you need to remember a date or a name. Pay by credit card.
Many people are afraid to use their credit cards for internet transactions.
However, if you do have a problem, you can dispute the charge through your credit card company. And to be quite frank, you'll usually win. So you have an advantage going in. Then email the seller with your complaint. Keep in mind that you are not dealing with a faceless corporation.