I would think hanging would be the best way to ensure no damage to organs, and they could even claim someone is dead, when only unconscious, to allow harvesting at their leisure. (hard not to believe someone is dead when their head is separated from their body :) )
Why would they buy guillotines when other forms of execution are virtually free (bullets and rope come to mind)?
Organ harvesting perhaps?
I would think hanging would be the best way to ensure no damage to organs, and they could even claim someone is dead, when only unconscious, to allow harvesting at their leisure. (hard not to believe someone is dead when their head is separated from their body :) )