Ronster said:

But the orders Vader gives suggests Boba had previously been given orders not to kill his bounties and did. So he did not follow orders and had to be warned specifically not to disintegrate this particular bounty and was very clearly like I let you off the last time you did that.

But if you like to think of Boba fett as someone who just flies around the galaxy following orders and that bounty hunter assassinations are as clean cut as what you make them out to be then ok.

I always thought he just reminded Fett (and the rest) that this was NO assassination job, cause it would be easier to kill the subject and bring proof back to collect the bounty ...

in the old west bounty hunters had often the choice "dead or alive" - somtimes dead was rewarded higher (depending on the criminal)

but in this case Vader needed his bait to lure Luke into the trap and test the device (carbonite freezer) on a living person - so no killing today ;-)