I believe they still wait for $5 mark for conversion fees, but I honestly don't know about the other. I'd think they'd loose money too on $1 books. But then again it's amazon, and maybe the just roll all the charges together with some special deal with credit card companies.
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UPDATE
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I guess I was wrong they do charge PER conversion now.
https://www.mobileread.com/forums/showthread.php?t=47284