INTRODUCTION: This is the first in a series of articles on selling books online profitably. Future topics include researching which books to sell; locating saleable books; and pricing and presenting them for auction or resale. The author is an online bookseller who makes over $1,000 a week selling books exclusively on eBay.

PART I: Which Books To Sell: INSTINCT
One of the first questions that arises when contemplating selling books online is, how do I know which books will sell? A quick glance at eBay book listings might discourage you from selling them at all because, sadly, the majority of books offered for auction ultimately receive no bids whatsoever. This is why it's crucial that you do your homework before spending the time and energy to list a book for auction.

Though this may seem woefully unreliable at first, the most important tool you have for identifying a saleable book is your nose, or instinct. Wherever you are - at a sale, in a thrift shop, a used bookstore, etc., - trust your nose. If you see something that catches your eye, it may well catch the eye of a buyer as well. A good rule of thumb is: if you pick up a book, look at it, put it back, and then at some later point pick it up again, it's time to buy it. It's caught your eye twice. There's something about it, perhaps as yet indefinable, that could produce a sale.

At this stage, assuming you know little or nothing about the value of the book you're looking at, try not to spend more than a dollar for any single title, preferably much less. It's quite possible to walk into a bookstore, spend $15 or $20 for a book, and resell it online for over $100, but there's no point risking a purchase like this until you have more experience.

Though it may seem imprudent to be buying books for the purpose of research - that is, with no immediate intention of reselling them - it's actually the quickest and most cost effective way to gain the experience you'll need, assuming you don't overpay for individual titles. If you take the trouble to develop your instincts, you'll begin to get smarter with your purchases very quickly and also notice that you're putting together and adhering to a set of rules that you may not even have thought about consciously. It's these rules that will help you weed out the 99.9% of books that you don't want to waste your money buying.

Several examples of silent rules:

1. Avoid books with more than one copyright date or evidence of additional printings.
2. Avoid book club editions (Book-Of-The-Month Club, Literary Guild, etc.)
3. A book with a dust jacket is much better than the same title without one (though it should be noted that some books are issued without them). Also, dust jackets that have survived 50 years or more are generally scarce.
4. A heavy book or one with a dense feel to it is likely to have more value than a light one.
5. A non-fiction title is more likely to have resale value than a fiction title.

As you gain experience, this list of rules will expand greatly, and the individual rules will undergo extensive refinement. (There are always exceptions to these rules.)

Once you've purchased your research samples, it's time to find out how you've done. The two best ways to accomplish this are by searching the titles on a book dealer search engine and by looking up your title on eBay closed auctions.

Because it's fast and extensive, one of my favorite search engines is abebooks.com http://www.abebooks.com. Another is Bookfinder.com http://www.bookfinder.com. While it isn't as fast as abebooks, the listings are more extensive and the search results are broader (including titles related to what you've typed in).

These sites and several others like them are a compilation of thousands of book dealers' listings. They can give you a rough idea of typical market prices for most books in circulation. I won't go into specifics now, but in general, you'll need to match up the specific copyright dates and publisher for an accurate comparison. Also, condition can make a huge difference, not to mention the presence of a dust jacket. Read the descriptions carefully.

Assuming you have located some comparable books on these sites, if the prices quoted are for the most part $15 to $20 or more, there's a good chance you may be able to realize $10 or more by listing your item on eBay. If the prices are lower than this, chances are you've got a dog. Another rule of thumb: in my experience, it simply isn't worth the trouble to list a book that sells for less than $10.

Now that you've separated the saleable books from the dogs, you'll need to dispose of the latter. One good way to do this is to take them to a used bookstore. Many of these outlets will offer you store credit that you can later use to purchase higher quality books for resale.

You can also appraise your purchases by searching closed auctions on eBay. More about this next time in Part II: Which Books To Sell: RESEARCH.