Proof of Funds via "Funding Partner"

[Matt Liu]

I have a Proof of Funds letter from my father, my "funding partner" that says
"xyz funds are available for immediate transfer or use by MattLiu at my discretion."

The problem is when I went to make an offer, one realtor said what happens if we are about to close and funding partner's discretion decided that it is not a good deal.
He makes a good point.
How do I get around this. Do I have to make the letter approve of the address each time?

Thanks!