[adekok]

Only if you assume that the share price always reflects company value.

The 80s were well known for corporate mavens buying undervalued companies, splitting them up, and selling the assets individually. The practice resulted in a net profit.

[portent]

Sure - if a stock is undervalued, then anyone buying it should get a good deal.

But that's bit different from saying that a stock buyback will always increase share price.