1) In the words of Buffet, "there would be no chance that a deal would be announced and that the buyer would then back off or start suggesting adjustments (with apologies, of course, and with an explanation that banks, lawyers, boards of directors, etc. were to be blamed)" [https://news.ycombinator.com/item?id=13906176]. Most of such re-negotiations can only be explained by screw ups in the decision making process or dishonesty of the acquirer trying to squeeze more from the tired owners.
2) Not screwing with the acquired businesses: they buy companies because they know their owner-managers are what made these companies successful, so it would be a stupid decision to replace them or change their operations.