Tenant moved early mid Feb paid full month's rent new tenant moved in 2 days later paid full rent. Since 1st tenant had a realtor she was paid for the 12 month's he was in the home, we deducted from his proration that he would have gotten back $651.67 the 3 month commission his realtor received and our fee which was $287.52, why should our client have to pay realtor fee for the month's he was no longer in the home. He received all security deposit back plus 354.15 pro-rated Feb rent. He think he should received the full $651.67.

It isn't a question of 'should;' it's what was in his contract with the realtor.
Many of them require full commission regardless of breaking the lease.