buyer's broker cash back - is there a form?

[Sundar Krish]

Hi,
I am a buyer/investor. The listing agent at one of the homes I found by myself and intend to buy is offering me 1% cash back from his total 6% commission, if I do a dual with him. It sounds like a win-win situation,
1. Is there a way to get a written statement for this (any CAR forms) instead of just relying on this at a verbal level. I do not know this realtor before, nor I do have/ intend to sign any sort of buyer/broker agreement with him that extends beyond the domain of this particular home.
2. Also I want this to be fully legal and fully disclosed on my HUD and be used towards my downpayment/closing costs. I am aware that some lenders do not approve his sort of cash back at HUD, but is there something else I need to be aware of and watch out for.
Thanks in advance for your valuable advice.