Not a white knight as I've not seen her.
On reflection of reading OPs review, I can understand that frustration. I've never reverse bidded on AW so this went over my head when first reading it.
However, I still feel a negative is harsh, but then I'd be a hypocrite too as I've negative reviewed WG's for wasting my time and a punt not happening.
In other words, my first message was pre ejaculation. This one was post ejaculation and now I can think straight from the punters POV.
She reneged on a deal. She caused inconvenience.
He’s not being cheap. Her normal rates are irrelevant. If she had bid with her normal rates he might not have gone through with the booking.
There are some reverse bidders who deliberately display high rates and will bid much lower. And many if not most reverse bidders will bid lower than the standard rate because they need the business and/or like the booking.
What she did is like asking the winner of your eBay auction to pay significantly more. You can refuse to send your item but you will rightfully get negative feedback.
White knight maybe?