If Edinaq realty signed the agreement your nicece may not have the authority to undo the agreement. If the agreement states that a commission is due on sale then you will need to pay that commission. The money became due to Edinaq once the sale was completed. It is not possible for a realtor to "kick back" the commission to the purchaser.
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Attorney
OH/TX Practicing Attorney focusing on Family Law, Foreclosure, Landlord-Tenant Issues.