#1: Books that have low competition, high demand, and a high cover price.

This is more of a way structure your searches than a book category.

Low competition: The lower the total number of offers for sale, the lower the FBA competition.
High demand:  We want the book to sell reasonably soon.
High Amazon price: The vast majority of books are not profitable because the price to buy the book from directly is so low (remember, you can't price higher than Amazon).

That's the magic formula. ‍

#2: Textbooks.

The single more profitable category.

So textbooks tend to be the best and the reason is, and it's probably obvious, but the reason is that people that buy textbooks, students specifically speaking, need their books fast and oftentimes, they're not paying their own bills. So they're charging it to mommy and daddy or, you know, it's whatever, like scholarship they're in or whatever. And so, they're not afraid to pay $50 for a textbook they could otherwise get for $5 if it means they'll get it second day. Okay? So that's a huge one. And then, a disproportionate number of students are Prime subscribers. Amazon has a program called Amazon Prime Student that I believe, as of the last time I checked, is 50% off of what normal people pay. So anyway, point is a lot of students are Prime subscribers and it just...all those things come together to make textbooks just the best category for online book arbitrage. ‍

#3: Textbooks In Disguise.

The biggest category of all. The number of these probably exceeds "normal" textbooks by 3 to 1.

What are these? These are books that don't look like textbooks, but they appeal to students, their primary market is students, and (most importantly) they are subject to the same market forces that allow us to charge huge FBA prices for textbooks.

They are called "textbooks in disguise" because by looking at them, you would never know they were textbooks. This is what I call "the hidden iceberg of textbook profits just under the surface," because few know how to spot these.

If you understand how to spot them, it's like an iceberg of profits that no one else can see.

Once you learn this, it's like striking gold.

Endnote

The Number One rule of your book hunt is always the same: keep it simple. There is nothing complicated about online book arbitrage. All you're doing is looking for cheap books that you can resell at a higher price. That's the entire game.

- Peter Valley