From one  perspective, you want it genuine, he really means it - it not a pretence it is very real to him.
If you love hearing a slave begging, it is beautiful, as he bathes your ears in his pleas.
Not all slaves are the same, and the offer they best from different approaches, Begging for mercy versa begging for the things they want (not whining like kids). It also allows the slave to get deeper into the 'slave space' in his head so that he can get the most out of the experience.

As one slave puts it, "It was like a mantra, the more i begged, the more of a slave i was, i would do anything for my Master, i just craved him, and everything he dose to me".

Related

Fear

i obey without question, for if i am bad the cold wave of fear runs over me for what he might do, for he is all powerful over me. Sometimes i question why have I allow this man to bind me, as my heart races and i know i am here for his pleasure - not mine.

Reconditioning Dogs Expectations

when i was a puppy  i was bad because i did not know any better. Master now had trained me will, i obey without question, i have learnt what is required of me.

Breath Control 

Where a little bondage helps, this will help his discover the power that his Master has over him and develop a level of trust that other techniques rarely deliver. Its also allows the slave to discover more about himself and his own self Mastery.

Domination

Resistance is useless. Whatever i do to defend myself it is hopeless compared to the might of Master, whatever i do, he will always win - that has been deemed by God himself

Discipline

Without this i would stray, my performance as a slave for my Master would suffer, and i could not consistently give of my best to my Master - as he deserves nothing less.

 

Bliss Elevation

Bliss Elevation there is no other place for me than the be kneeling before me Master. Every use me makes of me furthers my devotion to him.

Additionally I love to hear my slave beg to cum, to end the torment of sexual frustration, of course they are in bondage otherwise their balls would have been empty the moment I turned my back. As part of his training, he quickly realises that the moment he stops begging, that when you stop wanking him, he begs full on with total commitment and passion to the moment that he shoots his load. The finish up with making him eat his cum.

You need to ensure that he develops balance and poise, and becomes fluid.

This is part of the physical training of a slave