Does the lease address the $50 a month 'rent concession' if the terms are broken? Does it state that the 'rent concession' is to be paid back if tenant defaulted on terms of lease? If this was verbal as you say and the landlord accepted rent in the lessor amount, than new terms have been agreed upon for the lessor amount. What needs to be done is run this by an attorney for advice, perhaps an attorney in your company can help you arrive at an agreement between you and the landlord.
Yea... I don't want to bother with an attorney, but he's really pissing me off now after finding out he's advertising the place available July 1 when I've already paid June 1-July 31.
There is nothing in the lease about this concession at all. The lease amount only states the agreed upon rent at $50 lower than he initially asked. No mention is made of a repayment in the early lease termination section.