[aetherson]

Amazon isn't a monopoly, it has 8% of retail in the US.

There's no real evidence that this trade was made by Buffet himself, and it's part of a general major sell-off of Amazon that transparently did not temporally align with the idea that Amazon's retail business has suffered a decline in quality.

This is the market making a (reasonable!) judgment that it lacks confidence that Amazon's capital expenditures will pay off.