You don't have to buy and sell one book at a time
BTW, I would never try to take a book with a $4 cover price and try to flip it for $10 including shipping.
-slym
For Larry, I bet he paid $2 or less for the book. Consider that he normally only makes $2 per book. An $8 profit is fantastic (heh, no pun intended). For Larry it's all about volume. How much time do you think it really takes to post a book on ebay then prep it for shipping? 20 minutes total? That's $24 an hour. And consider he probably is paying someone $10 an hour to do this for him. This is why he likes $10 bill books.
*disclaimer - I have no idea how much Larry pays for his books or his employees. Just saying, $10 modern books are WELL worth his time. And could be worth yours too if you have the process of posting and selling books down.