In a few high-profile markets, prices seem to stay far above average cost even though there are tons of competitors.  There are thousands of credit card issuers, but the average interest rate is 18.26%.  There are over 100,000 real estate brokerage firms, but the default commission remains 6%.  Sure, unsecured credit has a high default risk, but high enough to justify an 18.26% rate?  And why on Earth would it cost $60,000 to sell a million-dollar home?

From the standpoint of economic theory, s...