As for the realtor, the commission is paid by the seller, so not sure how he's offering the buyer a discount on something she doesn't pay anyway.
Second, the buyer doesn't pay the realtor a commission, the seller usually does. If the deal doesn't happen, he doesn't get paid. Period.
Third...the buyer doesn't HAVE to buy. If she can't afford it, then it's easy to back out of the contract over loan conditions. (if she doesn't have down payment $$ she likely can't qualify for a loan).
But again...this sounds like third hand info, and it's hard to give you good advice when all the facts aren't available.