I've had to adjust prices of used books I have for sale lately. After working hard to become the price-leader on Amazon Marketplace, I did a little research and found that books in 3rd, 4th or 5th place in my particular book niches seemed to be listing their titles at least 25% higher than my price -- and sometimes much more.
Another way to stay aware of discrepancies in pricing which could be hurting your bottomline profits is to go to Inactive Listings on your Amazon Seller Account, and compare pricing in column to the right of your Sold Book Listings.
I was amazed to find that some books were selling for nearly double of what I was selling them for.
Check that: They were LISTED for twice of the price I had sold my book for.
There IS a difference. My book sold. I was paid. The competing book is still on the shelf waiting to be sold.
All I'm saying here is that it pays to nudge your sales price upward when you can, and don't always try to be the lowest price. Here's a snapshot of my seller's page detailing some of the wide price swings, as well as the competitive pricing used book sellers battle everyday online: