After reading some of the comments on the Shocklines thread on this issue I decided to have a go at uploading a couple of items onto Amazon. The process is quite different to FifoBooks and I had a few problems to start with. But I soon sorted them out and managed it. There's a review period of 48 hours before new items appear on Amazon.
I uploaded Sendings. I had to price this at $2.99. I couldn't price it lower than this. Likewise, I couldn't upload The Worst of All Possible Places as free, so that's $0.99, the cheapest I could set it for.
Anyway, that's something else for me to keep an eye on now. It could be a good comparison with the earlier uploads.