I can’t afford to buy a block of ISBNs from R.R. Bowker ($275 for 10). I found a company online that is selling single ISBNs. I didn’t think that was allowed?
You’re right. An ISBN owner can’t re-assign the rights of an ISBN to another. There are indeed naughty companies that are buying blocks of ISBNs and then trying to resell the individual numbers for a profit. In the end, the author is sorely disappointed because they were not and will never be listed as the publisher under that number. R.R. Bowker has posted information about this problem here: