Fair market value is different than market value. Market value is what is decided by the market. Fair market value something different:
If I'm selling a 3 bedroom house for $250,000 because other 3 bedroom houses are going for that, then that's the fair market value. If someone offers to buy it for $50,000 and I accept because that was the highest bid, the market value was $50,000 - much less than the fair market value. I also would have gotten fleeced on the deal.