Originally Posted by Xenophon
The thing I usually look for is having at least three* market players who are sufficiently competitive to matter. Book-selling, even on-line selling of PoD books seems to have that: Amazon, B&N's marketplace, plus the aggregators like ABEBooks (and similar businesses).
*Works best when at least three are individually significant, but you can get away with filling the third slot with a whole mess of smaller players (considered as a group) as long as the smaller players are relatively easy for customers to find. Or so sayeth the economics and public policy papers I've read. Your mileage may vary -- remember econ is the dismal science, and public policy is worse than that!
P.S. Of course the "three players" rule of thumb assumes that the players actually compete, rather than trying to do the oligopoly thing. In theory the U.S. Justice department and the Federal Trade Commission are supposed to keep track of that. Further, deponent sayeth not.
Hmm. It may be unclear if Amazon are a sufficiently large enough player to be considered abusing their power. However, I'd have expected it to be the case. I couldn't readily find market share percentages around - nor is it a clear case that 20% is always enough and 18% is never enough to count.